4 speed conversion

Okay, if you have the 5.125 retainer you should have the 833 overdrive or O/D transmission. You cant put a smaller bearing retainer on the O/D trans if I remember correctly.

Best bet is to find an O/D bell housing. Someone here will have one.

Second, i believe you can machine your bell to fit your trans. Someone here will confirm that.

Or you can find yourself a standard 833 trans with the appropriate bearing retainer. It will be either a 4.805 dia or a 4.354 diameter. You'll have to figure out exactly which bell you have.