'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.
@Jim Kueneman Since you didn't answer the questions, what did you disagree with?