pauldub wrote:
The vast majority of shuttle buses that I've seen are built on the E-van platform. Just taking a quick look on the internet, I do see a few built on an F550 chassis. If you want a bus built on an F350 or F450, you might have difficulty finding one.
This is true. Shuttle bus builders like the E series (or other similar van) platforms for many of the same reasons that motorhome builders do. Perhaps the biggest of these is that the floor is flat in the front, and can readily continue flat through the vehicle. Getting a good even transition between a traditional truck cab area and the box is much less straightforward, if it's possible at all.
Maybe you could look for a step van to convert?