I have an open air element, so I plugged the vacuum line, kept the pcv valve, and put a breather on the passenger side valve cover.

I realize I should be using a breather having a one-way check valve, so as to allow gases to exit at higher pressure, but not allow atmospheric air to enter.

Anyone have any recommendations for one?

Thanks in advance

"The" vacuum line? Your engine has a bunch of vacuum hoses. Are you talking about the fresh-air inlet from air cleaner to valve cover?

That's crazy. You're defeating the purpose of the PCV valve, which is to meter enough suction to pull fresh, filtered air into the crankcase to dilute the harmful fumes 'n' vapors that build-up there, and to allow those fumes and vapors to be pulled-into the intake manifold to be burned with the fuel/air mix. Fresh, filtered air entering the crankcase is DELIBERATE, and NECESSARY for proper PCV function. The only time that hose has reverse-flow is at heavy throttle (unless the engine has excessive blow-by.)

You'd be so much better-off to remove the hot-air air cleaner, reinstall the OEM air cleaner and then assure that the air cleaner has a source of cold (ambient) air via the OEM ductwork. In winter, you could re-connect the Thermac system to prevent throttle-body icing, and in summer let the engine pull in ambient air.

Open-element air cleaners were obsolete in the '60s. Popular, but obsolete.

Okay, thanks for the info