You are confusing Apples with your Chevy oranges.
Valve cover issue and the Positive Crankcase Valve (PCV) can be explained like this: with 1967 engines and down, the engine was vented by a PCV in the sealed oil fill tube and air coming up the former road draft tube via an oil air separator canister in the lifter valley under the manifold. The other end entered either the intake manifold for vacuum or it went to a similar fitting on the base plate of your carburetor. After 1967 you have valve covers with holes in them for a vent tube and the PCV valve.
This where the vacuum for your power assisted brakes and the PCV cross paths. Both use the same manifold pressure: they either share a "T" fitting, or one uses the carb base while the other uses the intake manifold's barbed elbow that threads into a hole in the intake manifold. If you don't have a hole in your intake you can have your machine shop make you one or you can drill and tap it yourself.
You need a one way valve to add to the "T" fitting if you go that route so that the power assist booster always has a full charge of nothing (vacuum) to work with while the engine is off.