A couple of things here.
I switched to Castrol GTX(owners manual recomened brand) High milage 20w50 this past weekend, it quieted things down quite a bit.
The "marbles" you all are describing is ping if I think I know what I'm talking about. I had it , added octane booster, helped a little. It would only happen between coasting and full throttle. I have been adjusting my HEI dizzy for awhile. Sunday, eireka!, I turned it the other way, NO MORE PING! Schwinnnng!
One word of warning, those stock dizzy's get stuck in there pretty solid, I used a BFH and busted the dizzy housing. Good thing I was replacing it anyway.
Oh yeah, lucasoil rocks, I use it in everything now.