Some of the PD carbs have a separate bowl vent hose that supplies all the float chambers. Some do not, and rely on the overflow tubes not being blocked for proper bowl venting. There is still a balance passageway between carbs regardless. So, it should still be drivable with one overflow tube blocked, whether you have the separate vent line or not.
However, I don't know why you wouldn't want to correct an obviously improper repair?
Further, the overflow serves to dump fuel out of the carb if the float valve sticks open. With it plugged, the fuel level rises and fills the intake/cylinder, and washes the oil off the rings, then dilutes the oil supply. If the overflowing gas doesn't go toward the cylinder, then it fills the filter box, where a carb backfire can set it ablaze. Maybe you'll be lucky and this will never happen?
Cheers,
