Not sure I understand what you are asking, but an engine is not like a tire, there are many moving parts inside, Pistons need to be weight matched, same with the connecting rods, there is no way to properly balance an engine without taking it apart. The crankshaft needs to be spun up with bobweights, and the flywheel/flexplate is part of the 428s external balancing. Sounds like there is a fairly substantial weight difference with your new pistons. Sorry, but it should be taken apart and balanced properly.