2wd to 4x4 conversion

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Hey everyone, been a while but I have a question.
I'm thinking about.converting my 2wd C20 to 4x4. It's a 76 regular cab long box. The body and interior are in awesome shape.
I found an 81 4x4 3/4 ton with a good chassis and rearend with a 700r4 transmission with low km. But the body is beat to hell and the box is rusted away.
How rough is it to swap by body and 454 over to the 4X4 chassis. And is there any big differences in those years I need to k ow about. Judging by some of the research I've done. Pre 83 is pretty much the same when it comes to these trucks.

Thanks