360 or 318 magnum

im sure all this info is on this forum but im short on time, I ran across a 360 magnum and a 318 magnum from 2 '99 dodge trucks, same guy has them both. both the trucks have trans issues. a few quick questions were they all magnums or do I need to look for something in particular, will I be able to use the manifolds in my car (1971 swinger), obviously the 360 has the bigger displacement but which one should I try to buy, which one has better heads manifolds etc? I know its a lot of questions but I gotta act fast so they don't get gone we don't see a lot of dodge stuff for sale around here. he wants $300 for each, I know somebody will say buy em both and I would love too and may try but can really only afford to get one right now, also I have to pull it myself. thanks for any and all help.