1992 Pickup to 80's solid axle swap?

I had a 92 4x4 and the frame was rusted out so I found a 92 2wd frame in great shape. I took out the drive shaft and transmission and lifted the cab and motor together, swapped out the frames quickly, and sat it down on the 2wd frame. I think I now want to make it back 4x4. If I do I want to put a 80s model straight axle under it. With all that being said here are some questions:
1) Im pretty sure the 2wd and the 4wd frame is the same? Am I right? I measured allot.
2) I see i need to change the rear 2wd axle because 2wd and 4x4s are different but...
3) By using a 80s model in front I would I need an 80s model in rear? I dont see why I would. 80s and 90s rear axles may be the same. Im not sure?
4) There is no need in welding Dana's under it because im not lifting it, putting 38s on it, and rock crawling.

You may wonder why Im doing this but I bought the truck because everything was perfect other than the frame and it was rusted all too hell. One owner 80k mile truck. Im just trying to make it to what I want. If its too much trouble and a bad idea, Im not totally against leaving it 2wd as I have two other 4x4s.