Agree with FWB. As far as crank case pressure being relieved through the
oil drain back hole goes, I can't see that as being a problem because the CC and heads are so open. You could totally plug the drain back holes and the
oil would still drain back through the openings at the intake and heads. The valve guides would stay submerged which would cause smoking at some point but CC pressure still wouldn't have a problem leaving and properly baffled VCs still wouldn't puke it out like the OP is saying. I would look for something less innocuous than a broken motor and run the PCV with a baffled VC and good PCV valve. If that didn't help, then I'd look elsewhere. JMHO