[RichardJ]

Long post so I'm not going into detail on your variation.

Vacuum to PCV valve, closed fill cap and tube to air cleaner is called a " Closed PCV System"
At idle, vacuum is high, blow-by is low. Clean air from the air cleaner enters valve cover, mixes with blow-by and is pulled into manifold.
At WOT, vacuum is low, blow-by is high. Excess blow-by exits valve cover to carb, thru carb to manifold.
PCV valve adjusts for cruise and varying load conditions.

Vacuum to PCV valve and vented fill cap is called a " Open PCV System"
It can draw air into valve cover at idle and spew blow-by out at WOT.
Open systems were allowed on only a few systems on the first few years PCV Systems were required.
A Open System is only one step above a road draft tube.

Your Dad's 3" hose is good for sucking dirt into the rocker box as he drives down the road.

It's best to let GM do the thinking here. They know how to make it beneficial to the engine.