'66 Valiant Running Hotter than Expected

Jim Kueneman said
I have very light springs in it it’s all in by 2500 RPM more than likely less. And 75 to 80 miles an hour I’m probably turning 3000 3200 RPM.

Well then its not retarded. If anything slightly too much advance under load. So not the cause of overheating.

Mattax said
Is the pump and thermostat working at all ?
Test: From cold, remove radiator cap and start engine.
a. The pump should pull the fluid level down.
b. When the thermostat opens coolant will flow into the top tank.

Mattax said
Is the pump impeller matched to the pulley ratios? In other words is the pump turning too slow ?

After those two, then check the temperature difference of the tanks and/or hoses after a drive.