I got that radiator out by cutting the nuts off with a chisel. They are studs that came right out of the radiator with vise grips and muscle.
Looking back on the comments, There was no way I could get a socket on those nuts. There was barely room to get an open end wrench in there to get a hold of them. This is a 1940, maybe some of the later ones were designed with enough room for a socket after enough mechanics griped about it.