'66 Valiant Running Hotter than Expected

You didn't mention how hot it really got just where the needle was on the gauge. Of course bugs can cause blockage and heating issues. What's your 360 block like? Stock bore, has it been rebuilt. .030 over or more? What degree thermostat?

0.030 over, totally rebuild, cleaned decked, line bored, etc, etc... 180 high flow ... blanking out of the manufacturer....