Nice catch, GoKohlerGo. It may also be an old Eljer Canterbury 081-2400 or 081-2450. I can't tell, and they use the same ballcock and diverter (495-0260-00), as well as the same flush valve and flapper, so it probably doesn't make a difference. Some people online have the ballcock and diverter, some don't, and it's gonna run you $60-70 just for the ballcock and diverter. These are probably the nicest guys, even if they don't currently have the ballcock. You can look at the model numbers of the parts you want, then start your search. The parts numbers in their little boxes are the manufacturers' parts numbers. https://www.plumbingsupply.com/eljer-toilets.html
They also sell a nifty little tool for unscrewing the flush valve from inside.