James hit the highlights -- I spent quite a bit of time researching this before I went with the Toyota drivetrain.

First-gen Amigos were available with a 5-speed 2WD MUA5 and first-gen Rodeos were available with
5-speed 2WD MUA5 and occasionally, with the 5-speed Borg-Warner T5 transmission. The 2WD MUA5 had a long output shaft that made it too long, IMHO, for a good 4WD swap. I was more interested in the back end of the transmission to fit a low-geared transfer case... I'm not sure about the front end. The only way to tell for sure is to count splines, measure input shaft stick-out, and check the bellhousing bolt pattern.

There is MUCH in common between most 4WD and 2WD Isuzu transmissions -- the T5 is the exception, really. A local tranny rebuilder did a good trade rebuilding Isuzu 2WD transmissions into 4WD transmissions, from a good 2WD used tranny and a blown Isuzu 4WD transmission. Isuzu transmissions are pretty stout, but they kill pretty quickly if fed 90-weight -- but with separate oil sumps, often the transmission would cook before the transfer case, leaving a great 'blown' donor core for this kind of 2WF transmogrification.

Randii