Day two of the 64 Valiant

I'd also wonder about running hot coolant to the base of the intake under the carb. Factory heat riser directs most hot air away from the carb and out the exhaust after the engine warms up; I'm thinking you have hot coolant heating the carb all the time, and it probably heats up even more when you shut the motor off after a hot run.

I'd try bypassing that and running that heater hose directly to the firewall. Car will run like crap when cold, but it might deal with the heat better.