You are confusing the function of the breather and the PCV valve. An engine bottom breathes in and out and you need some way to allow fresh, clean air in because there is occasionally a vacuum created which is what the breather is there for. It has an internal screen to keep out dirt but lets air in. More importantly, you need to have a place for pressure to escape because there is a lot of gasses entering the engine cavity from the combustion process. You don't want to depend on the breather to do this 'cause there is a fair amount of oil in the vapors and it really messes up the engine compartment. Until the environmental awareness came along in the 60s, engines just had a 'road tubeí; a 1 1/2" piece of tubing that connected to the engine lifter valley and extended down to below the engine near the road thus the name. Engine internal gasses were allowed to vent at will.
The PCV valve replaced the road tube and hooks the engine internals to the vacuum in the intake manifold and positively removes the vapors cleanly. Makeup air is let in by the breather so the 'air' inside the engine is much cleaner than the old days. Minor benefit is that the unburned hydrocarbons that used to be blown to the atmosphere are burned in your engine as fuel. PCVs are really a good idea all-round.
You have a few options. First, find a set of valve covers that have the necessary holes. Second, you might need to drill the valve covers for the valve. Put it in the valve cover opposite the breather so there is 'flow thru ventilation'. One final option is to put the PCV valve in the engine lifter valley if it has one separate from the intake manifold. Chevys donít' but early Chrysler hemis do - I don't know about Buicks.