Also keep this factoid in mind. This was posted some time ago by OldManMopar and I believe it's what was wrong with my rad
Radiator fins, over the years, from constant heat cycling and expansion / contraction, can 'crack' loose from the tubes. This does not necessarily cause leaks, and the tubes flow fine, but the radiator...........well it doesn't RADIATE anymore, at least not as much.
This seemed to be the trouble with mine. Running hot with the original 273 2-core, a rad shop claimed "it should cool a 360" NOT. Finally swapped in an "unknown" 73 slant six, also a 2 core, and the difference was dramatic.
