1967 Pontiac Firebird oil leak

Check the brather cap to make sure it is clean and also check the pvc valve. When engines run they can build up some pressure inside the crancase. If the pvc is dirty and cap it would tend to put more pressure making it leak. You might want to think about getting a compreesion check done, eliminating the thought of it being the rings. What it sounds like is that the breather cap and pvc valve need looking at. Quick check on pvc is by taking the valve ansd shaking it. You should be able to hear the little valve rattle when shacking it.