There seems to be only one brake disc  for all '80 to '85 model years, but more than one wheel bearing style (up to some time in '83, and then from mid '83 on.) I'm wondering why the same disc could house two different wheel bearings.

I also noticed that the Bus Depot seems to list different chassis numbers that correspond with the mid-year change of wheel bearings- they list the same month and year, but different chassis numbers. It would seem that if you're ordering early front wheel bearings from them, you might want to cross reference with another vendor to see whether to order early or late.

Ed in CT