Regarding test fitting, you'd still have to have these ground multiple times in fitting. Not that I've done the thick shim approach, but test fitting with original-type shims seems better.
Another problem, I think, is getting these to correct ID and OD without them crumpling. If you try to go oversize for the OD because the boss is gone, I think you may create a situation where you can't get a puller behind the main bearing. Maybe BSA included the boss for this very reason.
Richard L.