Is it not possible to document how it goes together when you take it apart?
Are you concerned that some else has been in there and put it together wrong?
I have taken some apart and found bearings installed backwards or lower than required class used so that can be a problem.
Surface grinder spindles are not complicated but they are picky about assembly and techniques if you want long life.
The big things are clean, very lightly stone, clean, clean again dust and lint free.
Ideally you indicate everything to sub-microns but most can't fix if out so that's not real helpful.
Finish steps best not done on the shop floor.
I don't have a clean room but the front office air is cleaner than the shop.
Oh, and make sure to put the correct number of ccs of clean grease into the bearings. This one is a often oops.
Don't overgrease. Bit by this one myself in my "non-understanding" days.
Making it run is one thing, making it run 40,000 hours is another.
When you get into a unknown spindle mark front on everything as you take it apart. Try to understand how it is all supposed to work and why.
The most standard setup is a preloaded pair up front and a radial on the back.
Note that my Okamoto is not that way so there are variations. In fact it has a spindle design that I'd call questionable.
Some Pope surface grinding spindles have some really complicated things going on with tapers inside the inner bearing races.
Bob