A vacuum leak will not cause the engine to rev that high unless there is a huge amount of excess fuel going into the engine too. If the carb is moderately rich, an air leak will cause a slight increase in idle speed. If the carb is on the lean side, a vac leak will cause the idle speed to decrease.
Check to make sure that the choke fast idle cam is not holding the idle up. The fast idle screw us down under the choke housing facing foward. If someone set the fast idle up too high with a wrong choke setting, then with the correct choke setting, the fast idle will be sky high.
Look down the secondaries and make sure the bottom butterflies are COMPLETELY closed.
Same with the primaries, look down and make sure they will close completely when the choke fast idle cam is pushed all the way down. If its NOT completely closed with the idle mix screw backed out and the choke cam down, find out why. Usually, its the fast idle screw adjustment.