Making a bracket

I'm matching a bracket for a Nema 24 stepper motor and the motor that I
have (and all the one I've seen) have a 1.5" diameter raised "boss" (not
sure if that is the right word) centered where the shaft comes out in the
front. Now, my question is, do I need to bore a 1.5" hole in the bracket
also, or can I just bore a hole larger than the shaft diameter? I plan to
mount the stepper using the four mounting holes in the corner of it. I was
concerned that boring a 1.5" hole would effect the rigidity of the bracket.
This stepper is a large 250 oz/in motor that weight 3 lbs.

Thanks,
Kory