Can you or have you tried running it with less preload? I would shoot for .010 to .015 hot wrench twocents
If not I would try it, it sounds like you got into valve float causing the valves to hit the pistons to me shruggy Are their witness marks on the pistons and valves? If so that needs to be taken care of to prevent future damages scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)