Don't touch the Allen screw in the vacuum advance. Just unplug it and cap the carb fitting as you said. Want you want is between 32° to 36° advance at an rpm of 2500 to 3000. That is accomplished by turning the distributor. Once that is done, the vacuum advance can be plugged in. If there is pinging, that's when you start adjusting the vacuum advance with an Allen wrench by turning it counter-clockwise. You don't want to go more than two full turns.
Do you know what camshaft specs are? This is what determines the 32° to 36° advance and 2500 to 3000 rpm. Milder cams on the low side, hotter cams on the high side.
If your cam is close to stock or 440 hp stock, use the lower numbers (2500 rpm and 32°).