210° @ Cruise and 180° @ Stop? What's Going On?

Are you running a thermostat? The system does require some restriction to keep the heads from cavitation.

Sorry for the delay. Holley 750 DP with mechanical secondaries

I noticed you said "fiberglass hood" in one post. does it have a scoop? if it does, and it isn`t sealed to the carb., hiway speed air pressure from the scoop can pressurize the engine bay and actually stop air from flowing thru the radiator. had two hotrods do this, and also a friends 500' crate motored p/u.