I have a couple of questions:
Milage- miles are extremely low for the year. Do you have access to service records to backup up the mileage? Is it possible that the speedometer has been replaced?
Tuning- I checked with the local diesel shops here and was told that the upgrade pieces intended for the Dodge pickup will not work with this engine. What have you found as far as upgrade options?
Transmission - can you tell us what transmission is in this bus?
Tires- sounds like the tread depth is OK. What is the date code on the tires?