i wouldnt say its a hard hard job at all, quite the oppisite infact, as you have nearly the best base sierra to do it too.
buy a 24v engine and loom, and a 2wd sierra front crossmember and assosiated parts, hubs ect. put the engine on the subframe. take your 4wd v6 gearbox and get a twincam sierra rear gearbox half put onto it. put your flywheel and a transit clutch onto the engine and job done, very easy and cheap!