I wouldn't cut the damaged area out. I'd go the other way. Rough it up, drill some retaining holes and epoxy it back to stock dimensions.
Oh, and anyone looking at these pics that has the inclination to modify their NSR cases, just take a look at the shape of the transfer entries and compare them to your "nasty" NSR cases.
Charles, there's a couple of horses hiding in them there cases. Better get your Dremel out
