The frames are basically the same, but you will need everthing that bolts to the frame to make a 4x4. The rear spring hangers are different, and as you know, the front needs spring hangers. All of the holes are not predrilled. You will have to locate alot of them. My opinion it would be easier just to get a 4x4 frame and swap everthing over.
Chris Lucashttp://www.73-87chevytrucks.comhttp://www.captkaoscustoms.com