'66 Valiant Running Hotter than Expected

30 degrees of total timing is not a lot for that engine. What octane fuel are you using? What kind of water pump are you using? Are you running vacuum advance (ported or manifold)? Retarded timing can cause heat buildup. Best to run max timing the engine will tolerate for both economy & performance.

Better do it now or I’ll forget.

Rebuilt (local friend) OEM factory pump with AC 6 vane impeller that was pressed on to the correct distance to the housing

Ported vacuum advance with NOS pot. Verified 52 degrees all, all in.

I have not seen a few degrees of timing make much difference based on the 318 experience in the Coronet years ago