Can you put 4x4 frame components on a 2wd drive frame?

[WyattTX]

In my area there is an 81-87 K10 swb that caught on fire, and is destroyed in terms of body. I have an 85 C10 lwb. I was thinking of buying this burned truck as a parts donor for a 4x4 conversion. It is my understanding that 2wd frames are the same as 4x4 frames, aside from the front suspension and steering component mounts. If this is true (please tell me if it isn't), I should be able to bolt and weld the 4x4 pieces on to my frame. I want to keep my truck a lwb, so frame cutting is out of the question. I could stretch the swb frame, but the burnt frame may not hold paint well. Thanks for any help in this matter.