I am getting ready to convert my supercab to 4wd this winter. At first I thought it was going to be really easy and everything would just bolt into place, well thats not the case! the big problem here is that a 4wd frame is diffent from a 2wd frane from the firewall up. Sure you could just buy a 4wd supercab frame and put our body parts on it but that is not what the OP and me are after. I have done ALOT of research and so far I have come up with 3 main ways to convert it. (I'm not saying these are the only ways to convert it to 4wd, this is just what I have read and come up with). You can lift the crap out of it to allow the tranny to clear the 2wd crossmember, only problem here is you have to fab up custom front and rear shock hoops or use blocks in the rear. (1979 Ford F-150 - Shocks & Hoops Installation - 4Wheel & Off-Road Magazine) If you are advanced in welding and fabrication you could cut the crossmember off the 2wd frame and then weld and fab a 4wd crossmember, leaf spring mounts, and motor mounts ony the 2wd frame. Or you can modify the frame. You can do this 2 ways, by stretching a regular cab 4wd frame or by cutting the 2wd frame at the firewall and the same from a donor truck and weld and brace it in place. The problem with stretching a frame is it will be weak in two spots in stead of one when you weld a 4wd front end on it. It is totally up to you how you do it, I am eather going to weld a 4wd front end on my supercab frame or I am going to weld and fab the components for a 4wd front end onto my 2wd supercab frame. I am not going to lift the crap out of it with front coil shocks because I want leaf springs up front for towing capabiltitys.
Best of luck,
Hunter