I have just finished the belt, idler, water pump service.
What are the odds of taking off the belt covers and finding the belt and crank perfectly located for a belt service. This car was ready for its new belt!
The cams pullies were off by 1/2...
Did you ever seal the plate on the oil pump? Maybe it’s not getting the right pressure till the oil warms up. Have you tried parking it in a warm garage overnight? Then you’d know how temperature or hardware dependent it is. My fear is you’re going to do all that work breaking the engine apart and trying other rings etc and then still have the noise. You might do better just finding a less noisy engine.