This is an interesting conversation. In thinking about it, at least for now, there are still a fair number of really nice if not perfect axle bells floating around. Does it make sense to do this repair if you need to take the rear out, remove the bell, cut it down with a lathe big enough to accept it, and then replace the bad surface with a sleeve?
For reference, I was able to purchase NOS '40 axle bells from Third Gen at Hershey for $175 for a pair. I'd have to assume you'd be over that in machining and parts alone.