swimpy,
Have you considered having the old motor rebuilt. I have a place by me that all they do is rebuild electric motors. I am sure if you look in the yellow pages, you can find one by you. Believe it or not our yellow pages has a section "Electric Motors - Dlears & Repairs"
This way you will not have to worry about finding the right one next time. If that fails Grainger may be able to get you a replacement motor, that matches the one you have. I am sure Groco, did not have this motor built to spec for them, most likely they used an existing manufactured motor.