Cleaning pistons

Wire wheel the tops, groove clean them if needed, and see if you can find a shop with a piston shirt knurler if that type.
Pressure wash maybe. They get oily and lightly carbon coated once in a running engine in the end. You mainly just wanna get any grit that could hurt cyl wall/bearings and a clean top as to not change any one cylinders cc/compression or cause preigniton from hot carbon.
I wire wheeled the tops of my KB's, brass toothbrushes the top lands heat grooves and deburred them all. Brake clean/ compressed air.