...there's an entire section in the 4th edition of Sutherland's Manual on interchangeability and fit for various cups and spindles. Unfortunately no one has a 4th edition any more, and those that do usually can't access an endless stream of cups and spindles, so it tends to be of limited use any more. I'm uncertain why a person here would tell you that the fixed cup needs to come out unless you plan on replacing it with something else like a sealed unit or a different cup. It's a whole lot of work for a perceived benefit of little or negative value if you can't reinstall it tightly enough.

I'm certain it is well intentioned advice, and if you choose to follow it, best wishes for your success.

I don't want to get into some big kerfuffle over the point, and nobody really knows what your approach will be right now. But the idea that removing it is somehow of benefit to some future owner, or even to you, over cleaning it well in place and reinstalling a spindle and clean, re-lubricated bearings has no basis in any "good mechanical practice" routine with which I'm familiar. It's usually a difficult enough job that it is better avoided unless required....which in your case it may or may not be. And believe me, I've removed plenty of them.