I haven't done this for awhile but..... put a piece of coat hanger in one cylinder hole, when piston is bottomed out. Rotate until piston gets to it's uppermost position. The coathanger, or whatever rod you use, should move
1 1/4" for 500, 1" for 472. Some Cad guy told me that and I have used it successfully when going to look at engines that have already been pulled, and displacement is unknown. Not sure what a 425 would read though.