[Mr 5 0]

I think it's a safe bet to assume the 'found' cars were considered junked and abandoned on drgoldfoot's private property. Every state has a different law on this but generally, if a vehicle is simply abandoned on your private property and it's ownership is unknown, it's yours to do with as you wish. After all, the car's former owner (a) obviously didn't want the car and, (b) he used your private property as a dumping ground. In most cases, the property owner would have to pay to have the junked car removed from his property. In this case, at least the property owner (or a family member) can get something out of the abandoned vehicle, which we will have to assume is worth keeping.

On the question asked: I also vote for the 351W engine as the best candidate for a fairly 'easy' transplant. Just remember that the car will need better suspension in front (14-year-old 4-cylinder springs won't do the job) and some mild beefing, such as frame connectors, in order to handle the 351 safely.