Best way to do it in my opinion is have the PVC valve on the top of one valve cover, and a breather cap on the opposite valve cover. This setup will ensure that you will be removing the nasty watery steam contaminates which likes to collect on the undersides of the valve covers.
Instead of the vented oil cap, you could plumb a hose from the top of the valve cover to a fitting on the air cleaner, providing for a cleaner source of fresh air than what a vented oil cap delivers.
