So the 4x2 body is good and the 4x4 body is shot? I'm not entirely sure what is what.
It's incredibly difficult to swap 4x4 and 4x2 in terms of the frames, you need to be very confident in your fabrication skills, even if you're bringing it back to stock.
You can swap body parts all day, but making a 4x2 frame into a 4x4 frame will take some work.
Oh, and you don't need to bump quite so often, only when it gets father back, like page 2 or 3 or something or after a few days.
*edit:
The swap would involve at the least a swap with a 4x4 transmission and transfercase. some minor trimming may need to be done and likely some wireing projects but it shouldn't be too complicated as long as you have a complete donor vehicle.
Then the engine cradle bracket wold have to be cut out. It is riveted in several places and I believe welded as well. You need to spread the frame rails (body is completely off obviously) and wedge the old one out, wedge the new one in, and be able to make sure it will go back straight again.
You'd need driveshafts, new front axle some of the obvious stuff and alot of back breaking work just to have a stock 4x4.
I'm going this route on mine mostly because it has sentimental value. Not because it was the cheapest option.