The choice is yours, but a lot of the engines you come across will have non Ford blueprint components, and the odds are, a compression ratio much lower than stock. So returning the parts to what FoMoCo intended for the 60's is a good scheme for a start. Late modle stuff does fit, but if it results in a compression ratio drop as it 9 times out of 10 does, its not a good option. The gaskets you get, the replacement pistons, the huge size of the late modle heads combustion chamber are odds against your favour, and to correct them, you need to know how to go about making those negatives positives.David and Dennis Schjeldahl from the Falcon Six Handbook are probably the ones who have covered it off best. They tell you what works best for the effort and engineering worth, and to fly in the face of the Falcon handbook is to court calamity.
I'd personally go higher compression, but keep the stock valve sizes, and get very good valve guides, springs, cam duration and lift and ignition set up. And follow the Ford Falcon Performance handbook on stock mods with this smaller valve size. Back cuts and the brothers suggested mods are the best options on a dollars per dollar basis.
CNC Dude is right, to gain air flow, you loose compression ratio becasue you have to enlarge the chamber to cope with 1.75 and 1.5's. 42 to 52 cc with an early log head and small valves makes almost as good flow as the later large log heads do with 58 to 62 cc and bigger valves, and you have compression up half to a full point with ease. I uses different rules for finding out how much hp you gain from compression ratio increses. In my book, a 15% gain in compression is half as much in gain in power if the engine is tuned not to detonate and wasn't before the compression ratio rise. The air flow gain from a later bathtub large log head is about 10 cfm at 400 thou lift at 25 inches of water, but if in getting that you loose 15% compression, you'd loose 6% of power by lower compression, or 7 hp at what should be 120, then the air flow gain and compression loss come close to cancelling each other out. In terms of math, each cfm improvment is worth 1.66 hp, so 10 cfm is worth 16.6 hp extra. Compression ratios are interesting, in that increases are potentially very great or poor, depending on how well in line the carburation and ignition is,
but if you go to 9:1 on the Falcon 6 handbook website,
then you''ll get the gross hp rating Ford used in the pre 1972 days, 120 hp. The old stock 1967 compression ratios were not as high as Ford stated, so any old 200 Mustang six could be anywhere, as bad as 7.7:1 with a thick composite 45 thou gasket and large 62 cc head, or as high as 10.4:1 with an early cylinder head which has been planed a few times to 42 cc, and still has a 22 to 25 thou thick factory steel shim gasket, and thats 102 gross hp verses 138 gross hp. Between the 35% difference in compression ratio is a 35% difference in horsepower by the calculator, with 120 hp at 9:1, close to the factory rating for the non California 67 Mustang.
I'd take the bare minimum off the head surface, then ream out the main carb hole from its punny 1.3" to a more flowing 1.75", and just plan to make your car run on low octane unleaded with about 9:1 compression. The chamber with a shallow composite or stock thin steel gasket will be close to ideal.
I have not used an Aluminum head gasket. Though have used alum gaskets for other purposes like an intake with good results.
