When Dan Wagner and I put together the 797 car, we put a 1/4" steel plate on the back of the engine, cut 3/4" thick blocks (threaded) that were bolted to the bellhousing, stood the engine on it's nose, and lowered the trans/input shaft into the pilot bearing. The MIG welder stuck the blocks to the plate, and the trans would bolt on/off.
Why did it work?....because the Getrag had a little less than an inch of shaft sticking out! With that in mind, here's one tranny setup that will work:
The Tacoma V6 5 speed (1995-2003) has a reasonable 4-5 gear spread. The 4Runner/Truck 5 speed (1988-1994) has the same basic trans, but the input shaft and bell housing are 1 1/8" shorter. That means you can use the "short" early V6 bell housing on the Taco V6 trans and have 1 1/8" of shaft sticking out. That is 3 sheets of 3/8" aluminum or steel...one sheet to bolt to the engine, one to the bell housing, and one to connect the two together. You've just adapted a 5-speed to whatever you want....with a bandsaw and a drill press.
It also moves the clutch release fork to the right side of the bell housing, which really helps the tight cockpit in a roadster or whatever.
If you need a bigger Overdrive (20%), use the Supra Turbo 5-speed (1986-1992). It takes the early truck V6 housing, and has the same input shaft length as the Tacoma V6. The pic below shows the Supra trans with the early V6 bell housing (for mounting to the V6). I made the spacers to get a bell housing with clutch fork on the right side (we put a supercharged Taco V6 in a 1978 Corolla).
Clutch disc for these trannies are available from several suppliers, with "grippy" stuff to take the power. On the dragstrip, these transmissions would go most of a season at the 500 HP level, in 3000 lb vehicles on slicks.....probably good enough. Pretty cheap part in the junkyards, these days.
I don't know of other transmissions with bolt on bell housings (in different lengths), but maybe someone else has an idea.
Regards, JimL