If you install the HH PVC setup you shouldn't "need" breathers in the valve covers, however as Skip says the wouldn't hurt. The whole idea would be to duplicate a modern PVC system yes, I believe you would want a sealed oil filler cap. Adding breathers to the hemi in my 32 is one of the things I intend to do when I get time. Good angled ones are a tad pricy so I'll wait till I have the extra cash. I did use a standard style PVC system on the 331 I put in my truck along with breathers.
Never pick a fight with an old man. If he is too old to fight, he'll just shoot you. - Anonymous