This is info gathered together from our many site members who generously gave their time in detailing their experiences plus great pictures all in one place to try and clear up and simplify the info on the small Six block differences.
The Summery of Ford Small Inline Six Block Differences
1. All the early small six blocks built from July 1959 (for the first year 1960 Falcon / Comet production run) to end of 1965 model run with block numbers C0DE to C5DE. These early 144, 170 or 200 blocks will only have the single bolt pattern for the small six bell housings that were only used with the 8 1/2 inch clutch and 132 Tooth "Dog Dish"/ Stepped Flywheel, and 3 Bolt Starter in the Cars, along with a 2.77 Trans. All of the Two Speed Ford O Matic / Merc O Matic's Cars also used this same small pattern Bell Housing too with a 132 Tooth Ring Gear, and 3 Bolt Starters. See Post #13 below for the latest info of the 3 proven ways to install the later 3.03 Top Loader Manual Transmissions onto these early Small Six's with a single Bell Housing Bolt Pattern Blocks and have more to drive Car.
2. In 1966 the Prefix C6DE block was the first to have a Duel the bolt pattern these can use the larger Bell Housing's for the Manual Transmissions along with the bigger 9 inch clutches and larger 136 Tooth Flat type Flywheel's and it also makes it easier to use the better Transmissions. The Duel Range and Select Shift C4 Cruise O Matic's still used the same smaller Bell Housing bolt pattern until the end of 1981 (there were also some High Mount Starter Blocks used in 1982 & 1983 too). Though I can't prove it at this time I think that all the high mount starter 170 and 200 blocks made in 1966 to end of production will likely be the Duel bolt pattern blocks with Prefixes of C6DE, C7DE, C8DE, C9DE. So they can all use either the larger pattern Bell Housing's for the 9 inch flywheel clutch combo or still use the small pattern Bell Housing's and stepped Flywheels. All C4 transmissions from 1964 to the end of production 1981 used the same smaller bolt pattern Bell Housing size as the other Small Six Automatics did so they can be fitted onto those older engines. Note: So far I have not worked on, found, or seen any pictures of any Large Single pattern only Prefix D0DE to D9DE series blocks or one that was not drilled and tapped with both patterns, at this point I don't believe that they existed. These later Duel Pattern 170 & 200 Six Long Block's can fit into an early model 1960 to early 1962 Cars with the either the smaller Bell Housing's (a Manual or an Auto Trans) for a Direct easy bolt in or with a small amount of Hammer work to floors and the trans tunnel also be used with the bigger 9 inch Flywheels and Larger Bell Housing for one of the better Manual Transmissions. There is no trouble in fitting them into with the Larger Bell Housings into the mid 1962 & 1963 up Cars. Note that on many 1978 to 1983 200 Six engines the oil pan and oil pump pickup tube out of the Fox Chassis cars is the wrong one to be able to fit with the cross members of the 1960 to 1977 pre Fox Chassis cars and will need to be swapped out to the early style 1960 to 1977 (a few later models up to 1979 will also work) to fit into the early model Chassis you will need a 144, 170, or 200 Front Sump version Oil Pan and Oil Pump Pick Up Tube. If you have those from your old engine they will fit and work on the later model 200's.
3. Last are the more rare two year only 1982 & 1983 200 Six Big Bell Housing blocks with a low mounted starter these resemble 2/3 of the small block Ford V8's 6 Bolt Block Pattern and were used only with the C5 trans and a lock up torque converter (see C4 and C5 difference's). These blocks are not the best for swapping into the early model Falcon / Comet cars especially in the 1960 to early 1962 year models as the larger bell pattern is going to require lots of metal work and or floor and trans tunnel cutting and replacement to fit. Note also that as above that on many 1978 to 1983 200 Six engines out of the Fox Chassis cars the oil pan and oil pump pickup tube is the wrong one to be able to fit with the cross members of the 1960 to 1977 pre Fox Chassis cars and will need to be swapped out to the early style 1960 to 1977 (a few later models up to 1979 will also work) to fit into the early model Chassis you will need a 144, 170, or 200 Front Sump version Oil Pan and Oil Pump Pick Up Tube. If you have those from your old engine they will fit and work on the later model 200's.
In this below video below it covers the difference's between the Case Fill C4 157 tooth flex plate (this is the first one) and the Pan Fill C4's 164 tooth flex plate (in the second one). Pay close attention to how many bolts hold the bells on to the C4 case and you can also see there is a difference in the two cases, Note also that only the Case fill C4's can be used with our small sixes. Note also that a Case fill C4 can be bolt onto any 144, 170, and most of the 200 Six's since they can use the Small Six 1965 to 1981 Ford C4 Small Bolt Pattern Bell Housing, Block Plate and the 132 Tooth Ring Ring Torque Convertor's these are just like the older Ford O / Merc O Matic's used, they also use the same 3 Bolt Starters making it a Direct swap. The only thing that needs some work is the Trans Mounting into the Chassis and a little reworking of the Column Shifter Linkage or replacement with one of the new aftermarket Tilt Columns or you can also use one the Mustang, Mustang II or Pinto Floor Shifters if you wanted.
The 164 Tooth Bells can not be used on the case fill C4 trans as they won't bolt up and are not interchangeable with the 157 tooth Bells. The third trans is a C5 that fits the rare late 200 Six Big Bell Blocks discussed above (again its 2/3 of a 302 V8 bell) that were used in the Fox chassis cars like a 1982 to 83 Fairmount, Mercury Zephyr, Mustang, & Capri.
The difference's in both of the C4's cases and bell housing mounting, plus the later lock up C5's
4. All 1969 up to end of production in 1983 of the 250 Blocks are the same size and will have the same Block Bell Hosing pattern as the Ford 6 Bolt 289, 302, 5.0, 351 W, 351C, 5.7 V8's and the 240, 300, 4.9 Big Sixes. These 250 Six blocks can be swapped into the 1967 up cars using factory mounts they will also fit into the late 1962 to 1966 Ford and Mercury Small Six models fairly easy with special parts or custom made mounts. They have also been swapped into the very early cars 1960 to early 1962 though it's going to require some metal work that needs to be done in the trans tunnel, the lower firewall, and floor boards to fit them in. Edited 9 /04/2023 with latest additional new Info.
The Summery of Ford Small Inline Six Block Differences
1. All the early small six blocks built from July 1959 (for the first year 1960 Falcon / Comet production run) to end of 1965 model run with block numbers C0DE to C5DE. These early 144, 170 or 200 blocks will only have the single bolt pattern for the small six bell housings that were only used with the 8 1/2 inch clutch and 132 Tooth "Dog Dish"/ Stepped Flywheel, and 3 Bolt Starter in the Cars, along with a 2.77 Trans. All of the Two Speed Ford O Matic / Merc O Matic's Cars also used this same small pattern Bell Housing too with a 132 Tooth Ring Gear, and 3 Bolt Starters. See Post #13 below for the latest info of the 3 proven ways to install the later 3.03 Top Loader Manual Transmissions onto these early Small Six's with a single Bell Housing Bolt Pattern Blocks and have more to drive Car.
2. In 1966 the Prefix C6DE block was the first to have a Duel the bolt pattern these can use the larger Bell Housing's for the Manual Transmissions along with the bigger 9 inch clutches and larger 136 Tooth Flat type Flywheel's and it also makes it easier to use the better Transmissions. The Duel Range and Select Shift C4 Cruise O Matic's still used the same smaller Bell Housing bolt pattern until the end of 1981 (there were also some High Mount Starter Blocks used in 1982 & 1983 too). Though I can't prove it at this time I think that all the high mount starter 170 and 200 blocks made in 1966 to end of production will likely be the Duel bolt pattern blocks with Prefixes of C6DE, C7DE, C8DE, C9DE. So they can all use either the larger pattern Bell Housing's for the 9 inch flywheel clutch combo or still use the small pattern Bell Housing's and stepped Flywheels. All C4 transmissions from 1964 to the end of production 1981 used the same smaller bolt pattern Bell Housing size as the other Small Six Automatics did so they can be fitted onto those older engines. Note: So far I have not worked on, found, or seen any pictures of any Large Single pattern only Prefix D0DE to D9DE series blocks or one that was not drilled and tapped with both patterns, at this point I don't believe that they existed. These later Duel Pattern 170 & 200 Six Long Block's can fit into an early model 1960 to early 1962 Cars with the either the smaller Bell Housing's (a Manual or an Auto Trans) for a Direct easy bolt in or with a small amount of Hammer work to floors and the trans tunnel also be used with the bigger 9 inch Flywheels and Larger Bell Housing for one of the better Manual Transmissions. There is no trouble in fitting them into with the Larger Bell Housings into the mid 1962 & 1963 up Cars. Note that on many 1978 to 1983 200 Six engines the oil pan and oil pump pickup tube out of the Fox Chassis cars is the wrong one to be able to fit with the cross members of the 1960 to 1977 pre Fox Chassis cars and will need to be swapped out to the early style 1960 to 1977 (a few later models up to 1979 will also work) to fit into the early model Chassis you will need a 144, 170, or 200 Front Sump version Oil Pan and Oil Pump Pick Up Tube. If you have those from your old engine they will fit and work on the later model 200's.
3. Last are the more rare two year only 1982 & 1983 200 Six Big Bell Housing blocks with a low mounted starter these resemble 2/3 of the small block Ford V8's 6 Bolt Block Pattern and were used only with the C5 trans and a lock up torque converter (see C4 and C5 difference's). These blocks are not the best for swapping into the early model Falcon / Comet cars especially in the 1960 to early 1962 year models as the larger bell pattern is going to require lots of metal work and or floor and trans tunnel cutting and replacement to fit. Note also that as above that on many 1978 to 1983 200 Six engines out of the Fox Chassis cars the oil pan and oil pump pickup tube is the wrong one to be able to fit with the cross members of the 1960 to 1977 pre Fox Chassis cars and will need to be swapped out to the early style 1960 to 1977 (a few later models up to 1979 will also work) to fit into the early model Chassis you will need a 144, 170, or 200 Front Sump version Oil Pan and Oil Pump Pick Up Tube. If you have those from your old engine they will fit and work on the later model 200's.
In this below video below it covers the difference's between the Case Fill C4 157 tooth flex plate (this is the first one) and the Pan Fill C4's 164 tooth flex plate (in the second one). Pay close attention to how many bolts hold the bells on to the C4 case and you can also see there is a difference in the two cases, Note also that only the Case fill C4's can be used with our small sixes. Note also that a Case fill C4 can be bolt onto any 144, 170, and most of the 200 Six's since they can use the Small Six 1965 to 1981 Ford C4 Small Bolt Pattern Bell Housing, Block Plate and the 132 Tooth Ring Ring Torque Convertor's these are just like the older Ford O / Merc O Matic's used, they also use the same 3 Bolt Starters making it a Direct swap. The only thing that needs some work is the Trans Mounting into the Chassis and a little reworking of the Column Shifter Linkage or replacement with one of the new aftermarket Tilt Columns or you can also use one the Mustang, Mustang II or Pinto Floor Shifters if you wanted.
The 164 Tooth Bells can not be used on the case fill C4 trans as they won't bolt up and are not interchangeable with the 157 tooth Bells. The third trans is a C5 that fits the rare late 200 Six Big Bell Blocks discussed above (again its 2/3 of a 302 V8 bell) that were used in the Fox chassis cars like a 1982 to 83 Fairmount, Mercury Zephyr, Mustang, & Capri.
The difference's in both of the C4's cases and bell housing mounting, plus the later lock up C5's
4. All 1969 up to end of production in 1983 of the 250 Blocks are the same size and will have the same Block Bell Hosing pattern as the Ford 6 Bolt 289, 302, 5.0, 351 W, 351C, 5.7 V8's and the 240, 300, 4.9 Big Sixes. These 250 Six blocks can be swapped into the 1967 up cars using factory mounts they will also fit into the late 1962 to 1966 Ford and Mercury Small Six models fairly easy with special parts or custom made mounts. They have also been swapped into the very early cars 1960 to early 1962 though it's going to require some metal work that needs to be done in the trans tunnel, the lower firewall, and floor boards to fit them in. Edited 9 /04/2023 with latest additional new Info.
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