Notice the difference in the air cleaner connector (attachment). I believe this one is original GM with the clutch head screws. Your valve cover and your picture of an air cleaner is most likely the retrofit AC kit. Both versions are "period correct" I guess as far as originality. To do your valve cover functionally correct, the vents need to be blocked because it defeats the purpose. Do you have a PCV valve on the draft tube or intake manifold? It's also possible your PCV is the "closed" type system (attachment).
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
