1920 has a leak in another place

I think you'll need that hole open to get the acc pump to work correctly. If it's sealed tight, the diaphram won't move like it should. Put in a good quality kit and check for leaks now and then. I guess if you were really worried about it you could drill and tab that hole for a fitting and then run a tube up into the air cleaner so fumes and/or gasoline will be routed there instead of dripping down toward the exhaust. I'd be more worried about bowl leaks with a 1920.