If there is a cover on the bottom of the bell housing you can pull the trans and not pull,the bell housing.
As for a clutch, I'm not sure where you live, but most cities with 20k or more people have a place that can rebuild the clutch and get you the disc you need. That way, you're not guessing if you have to correct parts.
For something like the bus you are working with, it's easier to use what you have and get it repaired.
Obviously, you didn't pick the easiest of rigs to work on. Or the lightest! That would come under the heading of heavy pig right there.
