Would the hypothetical guy want to make money or enhance historical knowledge...or both...or neither?
Excellent question.
I think the first thing the hypothetical guy would like to do is somehow, some way, get info/verification of what exactly it is he found.
The age, the style, possible origins, that sort of thing.
But ONLY ONLY ONLY if it can be done without jeopardizing his friends property rights!
Does that mean the best thing to do is tie it to a brick and throw it off the Tacoma Narrows bridge???