Found another ST60 in the stash. Early model with no ears and two rings, tall head. The piston is cut front and back and will clear the back cover. I swaped rear covers and everthing clears but I still need to check total clearance from back of rod/crank pin to inner face of rear cover. Now here is something else I have noticed I was checking my Bristunt P/L sets for these ST60 engines , both P/L sets have the bottom of the pistons notched front and rear like the two ring piston. Have not assembled the Bristunts into case yet to check to see if there is any sub piston induction going on. Will put one in this early case , measure and check every thing and run it. Been wanting to try one of these Bristunts for awhile. If it runs good I will try to Tig on some muffler ears to the case. I will practice on a busted up 46 case I have to get the process proved. Don't won't to ruin a ST 60 case.