Here'* the best I can find: Superior is based in Lima, Ohio, and was mainly a school bus manufacturer. Now they focus on Hearses and Limos.
Here'* a good history lesson:
and here'* their current homepage:
Oh, and just if you're curious, here'* what usually comes out of Superior Coach:
If I were you, I'd give these guys a call, maybe they still have some records of it being built. Hope the resto project goes well! We'll be here if ya need us!