Yep, Heinrich's had a ridge too. I'd say about 1/8th inch was removed. That's minimnal. Anyway, it can be bad enough that the new impeller has nothing close enough to create decent flow. I still like the metal impeller after the rash of plastic ones that came loose killing at least one engine by overheating. With the metal ones, as long as you don't let the water pump bearing go bad, they shouldn't be able to do any damage. I loved it when the PO of Heinrich's 86 said it smoked a bit from the timing covers when he drove the car.

 

Yes Bill ... a whole new meaning to "burning rubber"