Got a couple of ideas- - - - -
It sounds like something has gotten on top of a piston, probably #1. Are all the valve seat rings still in place? I had a problem with a brand new MOPAR 383, when an exhaust seat came adrift on a dyno run. It ended up getting pieces into 4 cylinders, and necessitating a full teardown to get all the chips cleaned out. I'd reccomend the same thing with your engine. Once chips start moving around inside, it's almost impossible to account for all of them without doing a full disassembly. You'll save yourself a lot of grief in the long run if you do a detailed teardown now!
Jerry
