FWIW My engine runs 80psi cold with no issues.
I really don't see how oil pressure has ANYTHING to do with your valve covers leaking! If the seal you should be able to fill them to the oil cap with no leakage,
You said they are old M/T, my bet is wrong gaskets,not tight enough or hitting the intake.I run MP notched to clear the intake and thick Fel Pro gaskets with no goo, and the only time they have ever leaked a drop was because once I did not tighten the back bolt enough. If your rockers are getting enough oil , fix the valve cover leaks and run it.
Just my opinion...