V8 bellhousing

There are six bearing retainers that I know of. 4.350, 4.80 and 5.125 both small and large bolt pattern, so there's no reason for people to make rings or adapters. I always wondered about that, myself. And yes, your wheel hub comparison is a good one. You must run the correct bearing retainer. The standard 3 speed (A230) and the 4 speed OD have the same bearing retainer bolt pattern, so the OD retainer is a direct bolt on to the A230 3 speed.....and vice versa if you don't have an OD bellhousing. I have an A230 I was considering running behind my Hemi, because I have the original big truck bellhousing that bolts directly to the Hemi and requires no adapter plate. It also has the same pattern to accept the A230, but it has a 5.125 (OD size) bearing retainer hole. I took the retainer off one of my OD transmissions and bolted it right on to the A230 and slapped it on the bellhousing and it fit perfectly. Correct depth and all. BUT, it's not a 4 speed and it's not an OD. Plus, I would have some fab time in the clutch linkage because the clutch fork is on the passenger's side and would require some fab work, whereas the 500 buck adapter plate will bolt the later 4 speed OD bellhousing right to the Hemi. It's a decision I am still thinking about.