Boy that's good! Heavy pitting, like it was laying out in the woods somewhere. You would really need to inspect it very closely to ensure it was solid as is to ride. Maybe even ask the seller the nature of the repairs and how they were done, if he knows. Lord knows I couldn't buy a bike like that and not ride it at least some, one way or another!
One other thing I just noticed, looks like all of the repairs are brazed, I don't see any welds; could be further indication for condition of the original metal perhaps? I think you could still make it operable again, it just might need some more advanced structural repairs, that curved rear tubing mainly?