Old School vs Magnum on 86 Dodge W100

Welcome to the site! Glad your son is interested in the truck. I would think you could buy a running magnum from a local yard, CL, or marketplace for about 200 bucks. Most of these will run countless miles if given any care, so buying one with a 150k on it wouldn't be a problem. If you are bent on rebuilding one or the other, then pick the one that needs the least would be my 2 cents