question about these Old Pro stock valve covers

There are all kinds of ways to skin this cat, as crackedback might say. I was going to put vacuum fittings in my headers and never did. For the short time I ran mine, I simply ran indentical caps to the above, one on each side, with a hose down to "underneath" to act as road draft. Those blank bosses on the other ends of the VC are designed for PCV, although I don't know how they operated. There likely were some accessories/ hardware at some time to do that. any fitting you put in there, though, will suffer from lack of a baffle system