1971 CB750 Rear Brake Help

[KenCB750]

Anyone have some info on CB750 rear brake assy's.? I bought a used rim from a 1970 CB750 to replace the bent up one on my 1971 CB750. When I went to put my 1971 brake assy into the 1970 hub, it wouldn't go all the way in. Rather than recessing into the hub, it rubs on the outside of it. because of a groove machined into the hub. Everything I read says all Honda brake panels are the same from 1969 thru 1976, and the person I got the 1970 rim from, assures me it's from a 1970 parts bike he still owns.
Any info someone might have would be GREATLY APPRECIATED!! It's getting nice outside and I really want to ride my bike!!

[Re-run]

Do you have a manual? It should fit just fine. Maybe a pic of what part is holding things up would help.