In order to have a nice hole for these thing, I recommend reaming it out after drilling it a bit undersized. This is basically a 2 step operation and better performed in a rigid drill press. A 1/4" drill bit will almost always create a hole bigger than 1/4".
Here is a nice explanation on the topic in case you need to do a lot.http://awtarlab3.engin.umich.edu/wiki/i ... ing_a_mill
Personnally for a few timing pulley it will be a lot cheaper to just buy new one, and just save those in case you come across metric sized stepper.
Nema stepper motor mounting hole location are the same for metric and inch. Just the size and thread differ, for the shaft they either have 5mm or 1/4inch diameter shaft for the Nema 17 and 23. The motor I'm using is actually a mix of 4-40 thread for the mounting with a 5mm shaft.