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:
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