Given the choice of 381 (5.21L) or 360 (5.9L) I'd go with the 5.9L, but why not consider a late model Hemi? A takeout with engine, tranny, wiring & computer is easy to find, given the wide range of applications that use them (Jeep, Charger, Challenger, others). If you're wanting to go the donor truck route to get more than the engine & tranny, you don't want a 4x4. The transmission in the 4X4 is built to interface to the transfer case, giving outputs to both rear and front differential. To change it to 2WD you'd have to swap out the tailshaft unit to get rid of the transfer case interface.