John, either setup will work, as long as there's a way for air to get into the valve cover. After 1968, the "Clean Air Act" in the USA mandated "closed" ventilation systems that put air from the "clean" side of the air filter into the crankcase so there was no possibility of fumes from the crankcase getting into the atmosphere. GM's PCV setup in the 1950's did it to assure no "dirty" air could enter commercial engines and promote abrasive wear. If the vented oil filler cap has some type of filter built into it, the same thing will be accomplished.
Jerry
