I have a friend that had too much pinging and he sensed something was wrong after 6 months after rebuild. He pulled the engine back out and his problem was a cracked ring. That could very well have been what has happen to you with all the detonation you were having! So you think going down to the RC12's from 14's stopped your pinging? 14's
would have been way too hot for your engine, you may still want to go down to an RC10 with that compression you have you will need a colder plug. I am running those plugs in my 383 slightly modified engine with 9.3 comp. Good luck!