Can you interchange any parts from a 81 Ford bronco to a 89 Ford bronco?

Underneath, back of engine, passenger side.

Size. The Bronco is a full sized vehicle. The Bronco II is the miniature compacted version. The full size broncos came with larger v8 engines and the Bronco II was designed during the first gas panic...

No, the front end of 92 - 96 Broncos is completely different than 87 - 91 Broncos.

the axle is a shaft that goes into your rear end from one side with the wheel bolts on it and the other connecting into you rear end differential gears.

for manual trans. it is behind the steering wheel, for automatic it is on the left side of engine compartment near the engine.