crankcase ventilation question, 71 GMC 350

[rickf]

I have an engine from a 1971 GMC C20 Camper Special, it happens to be in a 64 Chevy C10 now. As far as I know, the engine is stock, except for 600CFM Holley on factory 4-barrel manifold, tube headers, and a Pertronix ignition.

My question has to do with proper crankcase ventilation plumbing.

The right side valve cover has a PCV and hose going to carb base (I assume PCV, maybe just a flame arrestor).

The left valve cover has two holes, one has oil fill cap, not vented.
The other has a mushroom style breather.

This strikes me as wrong. Having the vent on the left side effectively disables any kind of crankcase vacuum that is supposed to be provided by the stuff on the right side. And worse, it actually makes a flow-thru airway that is going to cause lean running, especially at low throttle setting.

What is your wisdom on all this?