Thanks guys.
Looking at the car again, the fuel line from the pump to the carb could be a contributing factor. It runs up from the pump, under the alternator, (touching the alternator bracket) then rests against one of the the heater hoses. Where it snakes around the distributor cap, the outer edge touches the upper radiator hose. I think the contact points are probably raising the temperature of the fuel line and the gas in it. I have a Harbor Freight thermometer gun. I'll probably take a few readings just for the info, then run a new fuel line. Space is tight in there. It is hard to stay clear of heat sources but my guess is that I am better off with at least some clearance away from things rather than resting against them.
I do want to run the Carter pump with the regulator and return line. I like the idea of having the fuel running in a loop.