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Maybe not directly, but I don't see why you couldn't find adapter plates for some of it. Not sure what all you're wanting to swap, but I think it's 80-96 that's interchangeable.
The front differentials are both Dana 44s, but the diff in a 91 is a removeable third member. The differential in a 79 is part of the axle. I am pretty sure the carrier inside a 91 third member can be put into a 79 differential, but the outside axles are totally different.
The rest of your questions require more details for answers. Which tranny?