Nice writeup. I think the minor case contours wouldn't get to me so much. It seems that with the 16520, for example (because I'm more familiar with it), they altered the case design many times over its lifetime and that service replacement cases today are themselves slightly different as well. Variances are found in lug thickness, lug contours, pusher notching on the underside, etc.
Really, I think, what this goes to show is just how amazing a DW based rep can be!