'66 Valiant Running Hotter than Expected

If you have 45+ degrees of timing at cruising speed, then timing is not your problem.

When I bought an Edel Victor SBC water pump [ 20 yrs ago now ], I paid $US190 for it. I could have bought a Chinese pump for $50....
What did I get for the extra $140? Clearances! Nice, tight clearances! If there is a gap between the imp blades & the casting, then you are giving the coolant an escape route...it does not get pumped into the engine...which is what is needed.

The pump also needs to be overdriven [ smaller pulley ] 10-20%.
More info here: www.stewartcomponents.com