Another long drive today and the valve cover was still high and dry, I can mark that off my punch list
So, to summerize, the hole in the overflow pipe is to prevent syphoning of the oil out of the rocker shaft(s) after shutdown. The clip, when installed correctly, partially covers the hole which deflects the high pressure overflow oil generated at higher rpm away from the valve cover vent slots and also serves to keep debris from entering the hole.
Very good.
