Does the car have a good fitting radiator shroud on it??? The first step in isolating the problem might be to install a mechanical temperature gauge and get some real numbers as to what the engine is running. Those old Birds are tight quarters under the hood, in traffic or idling they will build up some high under hood temperatures.... I had a 66 Fairlane with an FE years back with similar stalling problems in traffic. The problem was fuel. I used the second port on the regulator as a return line with a bypass pill in it as used in mechanical fuel injection. My pressure at the carb was 5 PSI. If the problem is fuel related and not heat related, there are a number of companies making fuel pressure regulators with a regulated return port now.