How to identify the bore kit on quad

you would mic the piston to find out what size it is ---------- if it were me I would send my jug to G+H have them mic , hone or bore to a new piston if needed , they will supply the machine work , piston , wrist pin , cir-clips rings and all gaskets needed to do the job for a tad over $200 ------- the cylinder can get out of round ( egg shaped ) , if you re-ring it , it may not last long