I am thinking ring also. I need to get it apart, just to see. If it was a ring or piston, I want to make sure there was no valve contact. I have no intention of doing anything further with the 400 unless it involved a larger crank, but there should be a world of good parts there.
The truck currently has 8 3/4 3.55SG and is running a 2800 stall. The only converter I have for a cast crank is a factory high stall. Not real sure where that would come in.
I may just go with my mystery cam. It ran and sounded good right up till the "PING". If I decide I want more, I could always put my 1.6 rockers on.
This clip is after the burn out, but before I knew it was smoking.
https://www.youtube.com/watch?v=bVyTXPVNuXII will probably use the performer (non RPM) that I have. That is unless I score a deal on something that I may use on a future build.
