I have the big block version of those covers. I had to drill my own PCV holes and I used a Moroso baffled rubber grommet(Summit part # MOR-68775) for the hole openings. The grommet leaked slightly at first so I pulled it out and put some black RTV high-temp silicone in the groove of the grommet, re-installed, wiped off any excess, and it's been leak-free ever since. Just be sure not to drill the holes too large. Drill it slightly too small and then slowly enlarge it with a metal file until you get a tight fit. I also found that the following Fel Pro gaskets worked beautiful with these covers:
Summit Part # FPP-1635. They re-seal wonderfully and look a little better than the cork. I think they're worth the extra money.
Good luck with your covers!
