Is your Coach on a Spartan EC2242 chassis w/Granning Air Ride Suspension?
That's interesting Spartan said they were discontinued. I may have to call them again about ours.
I'm surprised they couldn't give you a Firestone part number.
What are the part numbers for the crossover fronts and rears?
What part numbers did you have for the originals (for fronts and rears)?
Check this thread about the plate
Please do reply/update here with the part numbers (for front and rears) of the replacement air bags you get and if you had to add the plates.
Pictures would be great to, perhaps you may want to start a new Forum Thread and link that thread in a reply here.
If you have the Granning, you may be able to find that info on a plate somewhere on the chassis (we also have an additional plate with that info with all the manuals. Then call Granning, perhaps they can help with part numbers.
Spartan should be able to provide some chassis illustrations for your specific Coach, like the one in this Thread (Post #6):