OEM PCV Valve & Breather Cap, "65" /6

Does this engine have an aftermarket chrome valve cover on it? Those things can cause all sorts of trouble, as they are unbaffled.
As for the breather, You could run a "closed" system. Unless your trying to keep everything 100% stock looking. Summit Racing sells a sealed breather with an outlet to run to you air cleaner. Note you need a later model can/or weld a tube to your existing can if you don't already have it.
I would try a compression check; don't worry alot about how much pressure, but check to see that all mesurements are fairly equal between cylinders. About 10-12 psi is a good window for an older motor.
Compression on these things stink......Let's shave it down...8)
BBBanjo