Somewhere in my piles of "treasures" I have an old WW2 GI ring tool. It has a fixture to hold the piston while the ring groove is cut to the size of the needed ring PLUS the thickness of an oil scraper ring. The ring/scraper combination kept the ring from rocking in the groove. Never used it but probably was adequate at best but in the war years everyone had to "make do". Jerry is right about an engine doesn't know the difference as long as the specs are the same. I had an air cooled diesel Lambordini (not Lamborghini) Italian built air compressor that ran on two cylinders and pumped on two. A piston fractured and replacement was $800 so moved a pristine piston from pump cylinder over to a run cylinder and then used a $20 .040 over 272 Ford piston in the pump cylinder. When people wondered about imbalance due to piston weight difference I said nothing could be more imbalanced than an inline 4 running on two cylinders

Evan