500 cfm edelbrock carburetor...
Holley 390 (4160) is too much carburetor for a stock slant six. A stock super six set-up would give the best economy and performance for a stock engine.
If you have too much carburetor, or in other words a carburetor that is substantially flows more air than the engine can pump, the carburetor will suffer from a poor vacuum signal, and can’t supply the correct air fuel mixture needed all the time. In other words the engine will be running lean, than rich, than correctly depending on throttle plate opening. You will experience bog off idle, perhaps poor idle, and chances are good that if equipped with vacuum secondaries they will never open.