Winner, winner. Chicken dinner.
Use another of your good engines.
After all, what are you saving them for?
So GM - are these pictures from TWO different engines . . . or only one? I'm hoping only one engine gave up it's ghost. That piston sure does look like detonation killed it -- the cylinder -- appears it has had some issue for awhile.
Good luck building another engine - seeing those pictures sure sucks!
D