Strongly recommend that you have one installed and the breather too, motor will build up pressure inside and at best blow out a rocker cover gasket, at worse all the seals will start leaking.
Dredging up an old topic because I came across it and I have always wondered ----
I can see that if you have closed valve covers, with no breathers at all, then you could have the issue you talk about....blowing out gaskets.
But if you have a breather on one or both rockers, effectively venting them to air, wouldnt that eliminate any possibility of blowing out gaskets due to pruessure building up? Even without the carb sucking in fumes, the pressure would not rise as it would escape through the breathers....
From what I understood, PCV was mostly an emissions change, keeping the vapors contained.