360 magnum. 1 piston lower in cylinder??

No marks on piston whatsoever. I sold the heads a while back and the guy needed them ASAP so they should be installed and running on his vehicle by now. He was a mechanic by trade and they looked really good. I did check the indexing of the crank as well as Piston to top of block at TDC. All good. Bearings looked good as well.
Good enough or is there something else I should check?
Crazy stuff, can't think of much other than hydro lock that wouldn't have left some sort of witness marks on the piston.

Thanks for sharing.