If you must go diesel, you're better off just finding a truck that came with one originally. Aside from having to change the fuel tank, fuel lines, wiring, and a possibly brakes (vacuum pump or switch to hydro-boost?) you're going to have to fabricate motor mounts or find a donor chassis in the junkyard and torch off the mounts on that frame. The bellhousings are totally different, so you're going to need a different transmission as well. That means you're probably also going to need two driveshafts.
IMHO, I think your most cost effective solution would be to find a 360 magnum, punch it out .030 over and drop in a scat forged 4 inch crank. That brings you to 408 cubes, which should put out plenty of torque for wheeling.
