How is your fuel return plumbed? Does the fuel flow through the carb bowls and then back to the tank or do you just have the return in parallel with the carb? If it's the second choice the fuel is just sitting in your carb until it gets used by the engine thus giving it a chance to heat up. Also definitely look into a carb spacer made out of either wood fiber or phenolic (plastic) at least 1/2" thick, and finally unless you drive your 440 in the winter go ahead and block off that exhaust crossover.
I swear every year pump gas gets sh!ttier, in a few years it'll boil off at room temp and 91 will ping like 75-octane:wtf: