In some cases, the factory-finish is distinguishable on the deck. A dial indicator is normally used, attached to tool that will straddle the center of the cylinder. A machined piece of steel (1/2" square will work), centered over the wrist-pin can be positioned on the deck, then measure the movement of the steel as you roll the motor past top dead center. Obviously, the still will move the dial indicator if any piston pop-out exists. It is legal to scrape carbon before measuring. Allowable is up to .005 pop-out. A bit of advise: Far bigger opportunities in gains though chassis tuning exist, so remaining a few thousandths of an inch under the max pop-out is my suggestion.