To be realistic, most year/body/chassis has more than one height available. Best way to describe this is a visual on the roof line just behind the drivers area. If you look at the profile of a bus (side view) roof line, and the roof drops about 3" a foot so behind the drivers seat, the interior height will be approx 6' high. If the roof goes straight then it should measure about 6'3" inside, and if the roof raises up some then you are looking at about 6'6" interior height.
These are generalizations here, exact measurements may vary some from one make to the next, but you'll find that to be close. I wanted to find a raised roof (6'6") for my Thomas Safety Liner, but locally the only thing they had was the drop roof at the time. Same bus, same chassis, same everything except the roof line is different.
Next time you are out and riding around (school is starting now anyway) look at the various buses and their roof lines and you'll see what I'm talking about...
You just might be a Redneck if...
...your motor home used to be a school bus!
...Your living room has a steering wheel!
...Your home has brake lights
1994 Jeep Grand Cherokee
1989 Thomas Diesel Pusher (Cat 3208/Freightliner)