I don't know if it'll help anyone but i've found a premade SchoolBus body exists in the usa.
Not a lexan shortbus for a monster truck, but a proper bus made of very thin steel. The details are a little light, but it beats my scratch building.
Jose Cuervo tequila at some point made a metal body conventional school bus. It's about 1/14 scale Party Bus with a wooden roof rack that held margarita glasses. Probably between 24 - 30" long. I didn't have a tape measure, or want to drop as much cash on it for a project i'm not ready for.
Lots of potential there. Maybe it stays party bus, maybe it goes like Partrige Family, maybe it goes chrome yellow and black with all the lights and stop arms and the doors operating. I dunno.
I believe it's like a 1990s International chassis, but i'm not up on busses. My district mostly ran Thomas and BlueBird pushers.