joiner, all school districts have school buses and therefore a maintenance shop. I'd suggest driving by one of them one day and talk to the oldest looking mechanic you can find. I'm sure someone will have experience and can help. A 5 minute conversation may be well worth the time.....and/or find out what company made the chassis. Freightliner or some other and go from there......just some ideas that may pay some dividends.
.....Joe Hand, you reading this?? I think Joe works on the big buses but not sure.
My chassis is a Chevrolet. It's a 1966 C-69 (60 series) to be exact. I just don't have it near me to look for myself.