I don't know about the McCoys, but when I was a kid, and I wore out a Fox or Johnson, we would do a frezer rebuild. Put a piece of dowl in the wrist pin hole on the piston, fill the piston with water, clamp a piece of wood on the bottom, and throw it in the freezer for a day. The freezing water would expand the piston a tiny amount, htem we used jewelers rouge to lap the piston into the cylinder. Worked pretty good.