Hi SuperCtruck ! I ended up not being able to use these covers and went with 1968 327 valve covers with a single PCV hole. But , I know Dino has a thread on a blue and white 66 that he made a simple PCV setup on for the script covers . You'll find that here.
http://67-72chevytrucks.com/vboard/s...t=dino&page=11 . I also have a good friend with a 1957 who drilled and tapped his intake manifold behind the carb and added a shield under the intake for a clean look. Hope this helps.