exhaust system pcv?
see this is exactly my same problem. I had breathers- three of them and one filler cap. oil is going all over my valve covers. & I didn't want to run oily air into my intake so this could be the compromise to only use one and not both?
You could start with one and a breather on the other side of the engine at first and see how it does.
The PCV is normally for low/mid RPM, so I would put it in like they say, and then be ready to limit the vacuum volume in case even one pulls too much.
A ball valve in the rubber line to the engine, or even a restricting orifice works for this.
Keep in mind that if you end up using both of them that you will still need a fresh air inlet.
I like to do this at the air cleaner so the fresh air inlet is filtered air.
This how I did mine for filtered fresh air.
I used a brass fitting with a small ring of PEX tubing (because I had it laying around) on the fitting first and then put the elbow through the base of my air cleaner, and another ring of the PEX and crimped it with a copper ring.
The tied wire is insurance against it slipping off and falling down the carb throat. (just drilled it and tied it)
It worked great because when I crimped the ring on it spread the PEX and sealed nice and tight to the air cleaner base, but still able to swivel for installation.