Chuck,
The answer is (as usual), "It depends." Commercial arbors for ø1.000 mounts have a 1.375 to 1.750 OD flange. I have a couple of homemade arbors with a 1.200 OD, though that is more a factor of having started with ø1.250 bar than any specific design intent. We need more information (drawings?) to really advise.