Anyone know Toyota engines?

A friend has a 1976 Toyota Chinook (small camper thing), with a 20R. The alternator is dead, and I know it supposedly is hard to match up alternators because they don't all plug into one another in Yota's. He also has a 1981 Toyota 4x4, with a 22R that just cracked the block, but has a newly rebuilt alternator.
The plugs in the wiring harnesses are different for both alternators. My question is, can we cut the plug out of the '81 and splice it to the wires in the '76 to make the alternator work? Or will it not charge because it is a different system?