New pistons / re-balance?

If you weigh a piston you changed against a new one and the difference is within a few grams you will be ok. internal balancing probably will not take expensive mallory metal as most new pistons are lighter than stock. Sorry to disagree Ramcharger but this is a low rpm stock build and if pistons are the only change the pads could be ground to match if the pistons are close to each other with just a scale if he has an old piston.