I have a 360 small block. Oil pressure cold is 70 psi, oil is 10-30. I have checked the shafts for the rocker arms and the groove is down front on the left bank and down rear on the right bank. I switched back to stock stamped steel covers hoping that would help. Gaskets are glued to the cover only. Motor is a mid 1980's. Head milled .020, performance cam and springs. Stock type flat tappet lifters, pushrods and rocker arms. I am frustrated. Any suggestions appreciated.

Do you have a PVC system hooked up correctly?

Yeah, sounds like high crankcase pressure. Does it do it when you have the oil cap off?

I will check that. It has a stock filter looking canister with a 5/8" house outlet that I don't have hooked up.

This is where you should start.

A correct PCV system starts with a vented breather cap on one valve cover and a PCV valve in the other connected to the intake manifold vacuum port or the large vacuum port on the base of the carburetor. This allows bypass pressure in the crankcase to relieved.