on my 327 I used a grommet from bbc valve cover pcv and it fit perfect in the road draft in the rear of the motor. then I silver soldered a 3/8 pipe fitting in the oil fill tube and screwed in a pcv valve and ran it to the carb. in the road draft hole I ran a tube to the under side of the air cleaner to suck clean air had work great and did not put any holes in the valve cover. Ed ke6bnl