Mini Sarter Help

I have just purchased a new toy it is a 63 Fury /6 3 spd standard on the column. Yes I know it is a b body but I didn't get the answer I needed on there site so I thought I would try here. The problem is the starter is finished and I need a new one. I picked up a mini starter from the junk yard to try but it will not engage. So I started comparing the starters and it has a larger drive gear than the original starter. I even went to Napa and bought what they had listed for the car and it had the same problem. It will not engage. It will be returned today. Any suggestions would be greatly appreciated. Thank you. Jeds67