I recently installed PCV valves to my 302 GMC running 3 Weber 32/36 carbs. One valve is on the breather and the other is on the rocker cover. They both connect to a common manifold that feeds into the bottom of the 3 air cleaners which were designed with plastic fittings for this puropse.
This setup does not affect the A/F mixture as far as I can tell. Before the installation, the car used to fill up with engine blow-buy fumes to the point it was uncomfortable to drive. Now the smell is completely gone.
