[LMH]

I can't comment specifically about 428 cranks but the practice of grinding a crank to increase the stroke used to be common in the VW world. The problems arose because the "inside" had the hardness ground off and added material on the "outside" wasn't hard enough either. I've seen a number of ground cranks fail in VW's in the past because of such grinding.
Of course, once manufactured stroker cranks started showing up, no body ground them anymore.
That was my experience with them but maybe the 428 crank is a totally different beast.
Larry