I've dealt with a few overheating problems, on both my truck and on the 41 Chev sedan. In the course of all this work, Stuart mentioned that these old bolts collect a lot of sludge. Since then I have flushed both engines, and he sure was right about the sludge. You might flush yours while the radiator is out of the way.
Another odd thing we noticed on the '41 was the thermostat: we had replaced it, the one we took out was rated at 180 degrees , the FLAPS checked their books and sold us what they said was the proper stat, another 180. Since then we have bought The Service Manual, which says that the original thermostat was 140 degrees. It sure looks better on the temp gauge now with a proper rated thermostat (the book said to use 160 with glycol, I believe).
Haven't I read here not to top off the radiator?
Karl

It may not be the easy way, but it is the Cowboy Way - Ranger Doug
Beware of the stories you read or tell; subtly, at night, beneath the waters of consciousness, they are altering your world. - Ben Okri
1953 Chevy 3100
1960 Volvo PV 544
1941 Chevrolet Special Deluxe