Back when I had a 2-pack-a-day Winston habit, I tested vacuum advance units by trying to blow smoke through them. It sounds like the vacuum numbers from the carb are about right, as the maximum vacuum will happen at a steady-throttle cruise. it will just about disappear at wide open throttle, as the spark needs to retard during acceleration.
I don't think a bad vacuum advance will do much more than give lousy gas mileage, as most of the advance is done by the centrifugal system and the vacuum just kicks in for better fuel economy at cruise speed with a light load.
The need to choke and/or pump the throttle to keep running sort of leads me to believe you're either dealing with a primary wire inside the distributor that is intermittently going open-circuit due to vacuum advance movement, or you're starving for fuel. Try this: Disconnect and plug the vacuum advance line so the dizzy doesn't move, and see if the problem goes away. If it does, change the primary wire from the distributor housing connector to the points.
Jerry
