If it was built many years ago, then you will have a tapered cly wall from the rings wearing more at the top where they load more. I just repaired a motor that someone had done just what you are talking about. It had too much wear for the new pistons to compensate for with the skinny racing rings and had a bad ring seal. We had to buy .040 pistons and hone it to the next size. I have done what Cab suggests and ordered custom pistons for the exact size you need. I’d take the motor apart and measure it exactly before I ordered pistons.