At least for grinders with brakes, Baldor has a manual on how to replace
the wheels. With brakes, the spindle nuts will tend to unscrew.
Anyway, here is the URL:

http://www.baldor.com/support/literature_load.asp?ManNumber=MN903a

It appears from the drawing that the washers are both machined and keyed
to the arbor shaft. The arbor nut is also cottered, to prevent
unscrewing.

Don't know how much of this carries over to ordinary Baldor grinders.

Joe Gwinn