The real thin aluminum ones? IMHO they are the worst valve covers ever made. Too thin, and too flimsy to not leak. I'm not surprised they have no provision for PCV baffles. They were mostly used on race cars where they were trying to save weight and, obviously, had regular breathers installed by the racers.
the stamped alum valve covers on the hemi`s were leakers too. we went back to the steel covers. (BACK THEN) you can buy all kinds of baffled pcv grommits , keep looking.