A local machine shop made the parts for me.
Larger bolts with larger nuts would interfere with the outer diameter of hub casting just inboard of the brake flange.
The ring keeps the rotor concentric with the hub.
I checked the clearance between the rotor bolts in the original application and the the rotor bolt hole diameter and found it pretty loose. It looked like the factory used the center bore to keep it centered so I just did the same.
