Sounds like you need my '70/72 4x4 SWB truck I'm selling
From what I know, If you are going from 2wd to 4wd, the easiest way to go is with a leaf-spring 2wd frame. The front Crossmembers will swap, but you still need to mount your shackels and such up front. I looked into doing this a while back but found it would be easier to do a bodyswap. However, plans changed once again, and I'm Step-Notching my SWB 2wd to lay frame this winter
Hope this helps some...
Kenny