I still have race pistons, that were made for the club, they are single ring and proper jobs, I'm sure I have std bore sizes and lots of over size items, before you purchase if your making a new engine make sure the welding/bronze welding has been done and the bore is ok, we always welded the inlet port then opened up the exhaust first, just incase you break through, that would need welding, then check the bore its amazing how much stress you introduce with doing this, also check it cold and hot by putting a blow torch up the exhaust port, amazing how much this changes the shape of the barrel, some carfull handling needed to avoid burnt fingers and we mad a contraption to hone the barrel in a vice with the four studs clamped up
my advice is to establish pistons after your barrel is finished.
regards Derek