[bobbader]

YES to grinding the nose of the water pump housing. That's the problem.

NO, NO, NO to the reamer. With all respect to Joe K ............... yes such a reamer IS available. But, any tapered reamer can cause worse problems if they cut past the point of making a "perfect fit" between the tapered hole and the tapered shaft. In my opinion, in this case, using a tapered reamer in an already cut tapered hole most likely will make matters worse.