I am invovled with a similar project starting in Boston. We are in the planning stages, but the research I have done shows that it is possible. I would make sure your filtering element/racor is changed often. We want to run on veggie too & have thought of adding propane injection. I have heard that it runs about $200 bucks & that it will give you almost instant power with a flick of a switch for passing & climbing. Instead of using multiple bbq type tanks look into an RV tank that mounts under the bus permently. I would pipe it with either marine grade custom sized propane hose/tubing or copper tubing with flared conections, it is only between 7-10psi so it would be the connections you would have to pay attention to. It being a bus I would look into adjusting your govenor as well. Skoolie.net has a lot of info.

Happy Rails!