a good place to look would be
vfaqs.comif you go to 1000 already answered questions and scroll down the left side you will see information about swaps.
if he has a late model 91 his transfer case will be a 23 spline, and your 90 will be a 22 spline. this is a problem.
another thing you might run into is that the td04 turbo (auto-provided your auto is a turbo) has smaller coolant lines than the td05 turbo (manual)
here are few other differences:
For 1Gs, there are several differences between manual and auto cars of the same year, aside from (duh) the transmission.
Auto 1G cars have
- smaller turbochargers
- smaller injectors (390cc)
- a 'power/economy' switch located next to the shift lever
- ECUs designed for the smaller injectors
- cams designed to produce more low-end torque [1G only]
Manual 1G cars have:
- bigger turbochargers
- larger injectors (450cc)
- a nifty little coin holder next to the shift lever, a fave place to put electronic widgets of one sort or another.
- ECUs designed for the larger injectors
- ECUs designed to produce less low-end torque [1G only]
there is a nice write up about doing your swap there for fwd's but i didn't see one for awd's.
I am not an authority on this subject, and am just using the vfaq's. the vfaq's has given me outdated information before such as the cuase for crank walking. do not take my information to heart, I just hope this helps.