Hi David,
Welcome aboard!
Things to keep in mind are the different bell patterns on the various I6 blocks.
The 144/170/and pre-66 200 blocks use a "small" 8 1/2" stepped flywheel and small bell.
The '66 - '80 (?) use a 9" flat flywheel and "mid-size" bell.
Somewhere around '80-'81 the 200 got the "big bell". With a few modification, it it supposed to be possible to use a 302/5.0 bell. I've never worked on one, so I don't know.
The 250s do use a 302/5.0 bell and the flywheel bolt pattern is also the same as the V-8. The flywheel is the same as the V-8 flywheel - except for the balance factor. Since the I6 is a balanced motor, you will need to use a zero balanced flywheel. FRPP has these.
Adapter plates are needed to mate a Ford pattern T5 to the small and mid-size bell. Modern Driveline carries them.
What follows concerns installing an S10 T5.
In my case, I had several S10 (GM pattern) T5s handy and found a different solution.
The engine in my Squire is a pre-66 200, so it has a small, 8-1/2" stepped flywheel and small bell pattern.
Several small pattern bells are out there, but the bell used behind the early econolines is an odd duck. It is about a half inch shorter, and has a Ford toploader transmission bolt pattern. In addition to the pile of S10 T5s I had an old toploader to GM/Muncie type adapter, which just happened to be a half inch thick.
The GM S10 T5 has a 1" x14 spline input shaft so I went through the centerforce catalog looking for a clutch that fit. Turns out there are quite a few 8-1/2" 1"x14 clutches available. They all have a larger spring pack than the stock clutch though. I had the flywheel face relieved to accomodate the spring pack when it was re-surfaced. The machinist didn't charge me much for the work, an extra twenty or so, iirc.
Another difference is the size of the T/O bearing shaft, the GM T5's is larger. I could have ordered a Ford T/O bearing shaft and installed it (they are interchangable), but I used an S10 TO bearing and just tacked the Ford clutch fork plate and spring to it in a few spots (once again because I had a couple S10 T/O bearings handy).
Once all the parts were gathered, installation was straight forward. Stock pedals worked just fine.
I had a driveshaft made with an S10 slipyoke at the front and a Ford 7.25" rear yoke in the back.
After about a year of use, I ruined the stock Ford pressure plate and was looking for a replacement. The small pressure plates are getting to be very hard to find, with most having been rebuilt several times by now. After some research, I ended up using an Alfa Romeo 215mm pressure plate. This required skimming .15" off the flywheel plate mounting surface. It's a great swap, making shifting a breeze.
A later 8" rear end swap required more drive shaft mods.
The T5 transmission is much larger on top than any of the stock transmissions used in Falcons and early Mustangs. As a result, the transmission can't sit as high in the tunnel. Everything will work fine, the pinion angles will need some careful attention. Even with the angles set perfectly, you may have driveline vibration at highway speeds. This is due to the working angles of the U-joints when the pinion angles are set to accomodate the T5's installed angle.
Some solutions are:
Drive around with the back of the car jacked up high (yuck).
Enlarge the transmission tunnel to let the T5 sit higher.
Lower the motor mounts and inch or two. This sounds fairly simple, but requires modifications to the bolt-in cross member and also requires flipping the steering linkages upside down (like in a 250 swap). With the front of he engine dropped you can raise the transmission enough to get friendly U-joint working angles.
A rear end ratio of 3.0/1 works great with the S10 ratios (first gear is 3.76/1). The Ford four banger T5s have an even shorter 1st gear of 3.97/1.
The S10 tailhousing puts the shifter well forward of the transmission tunnel brace.
Hope this helps.
Got your PM and thought I'd answer here.
Rick(wrench)