We'll, I'm looking at 2 FF transmissions here in my garage. Neither one has the bosses for the rear aluminum mount for a MK II. The FF was originally a MK 1 trans. It was popular on the early models (1978-1982). As far as I know, only the late (1983-1984) transmissions had the bosses (the thickened tubes on the side of the diff casing), to accept the later MK 2 style rear mount. If I'm not mistaken, only the 9A, 2H, and 4K transmission had those bosses for the mounts: basically, only the late MK 1 transmissions with limited slip had them. I had to find out the hard way: by assuming that the FF would fit into a MK 2. I ended up having to buy an ACN. It was a bad match for my 1991 Jetta, because I had a 1.6NA pumping out a mere 55 hp.
Anyway, the FF that I tired to put into my MK 2, and the ones I have in my garage, all lack the bosses on the diff housing to bolt up the mount. The MK1 used 3 studs on the pass side of the trans, the MK 2 uses 3 bolts on the pass side. The holes between the two models are offset by one hole. When looking at the FF in my garage, there is only 1 out of 3 of the bosses in place. This is not a matter of stregth, as much as it is about ease of mounting. You could mount the FF in the car, but you'd have to weld on some bosses and drill them out, or transfer the guts to a MK II casing.
So,either way, I doubt that your trans has the bosses for the MK 2 rear mount. It's possible I guess, if you happen to have found a late MK1 FF code that is actually ready to go.
As far as the rims, I was suggesting that if you can't get the FF to go in, you might want/have to buy one of the ubiquitous ACN (typo in original message), ASF, or ACL that came on about 80-90% of all other MK 2 gassers. All of these transmissions have 3.67 gears, but do have a .75 5th. I'd be reticent (having tried one) to put any of these transmissions on a stock 1.6NA, since the final drive really kills the power band. But, since you'll probably be pushing a lot more HP than a 1.6NA, then you might be good (maybe even perfect), with a 3.67 FD
The only drawback I forsaw, was that you had some large, and presumably heavy, rims on the car. The greater rotational mass coupled with the larger diameter, requires greater torque to spin the wheels. So, the 3.67 may not be geared low enough to get you optimum performance at low speeds. At highway speeds, you'll get great fuel economy. But takeoffs might be sluggish. The only way to find out how it will perform is to get your car tuned the way you want it, and try out either trans (with a 3.94, 3.89, or 3.67) final drive.
Let us know how it goes.
