If you can get a new piston, do you know a machine shop that will re bore the cylinder then you can get a oversize piston and rings. If not I would say its worth a try just new rings and hone out the high spots so the new rings can't catch on them. I have been there and done that. Some times you just have to make do with what you have. I had a old road-a- tiller this early spring I had to do that with, the customer has ran it all last season and as far as I know he is ready for next year. On that engine I had to use the piston over and just cleaned out the piston ring groves so the new rings were free to move. runs fine