Without the actual wieght of the old pistons you are just guessing, weight also includes the rings.
The KB 107's is used in my mag were lighter so mallory needed to be added to the crank.
Id be surprised if there was enough of a difference between the old and new rings to matter, but maybe that's true. I have the listed weight of the old pistons, according to Larry Shepard anyway. Is that not a good enough go by?
