I have put new rings (along with bearings down below) on LOTS of old pistons for everything from Minneapolis-Moline tractors to Porsches, but you can't just stare at a piston and decide whether it's ok with your eyeballs -- you have to get someone with good machinist's measuring equipment to judge the piston skirt wear, the roundness and taper of the cylinder bores, etc. If the bores are good, but the piston is just a bit below spec for diameter across the skirt where it matters, it can be knurled, too: this consists of using a special tool to raise bumps to bring the diameter back to spec., and it's a lot more durable solution than many would imagine.

But none of this is possible without the right tools and experience. When I was 40 years younger, I wouldn't have been afraid to slap in a new set of rings and bearings on my own machine (and only my own) without all these concerns and then see how it worked out on the track, because I had the energy to redo it properly for myself all over again if necessary, but that was long ago.