do your valve covers have breathers in them? you have have other breathers that hole isn't really needed and can be plugged.
stock there would have been a flared hard line stuck through a grommet in that hole, leading up to one of the big vacuum ports on the front of the carb. it is jsut for crank case evac.
a lot of people switch to breathers on the valve covers because having a feed like that puts a lot of oil vapor crub into the carb and the engine.
good luck with it
