My brother drives trucks for a living and has a CAT. His truck has over 1 million miles without an overhaul but has had numerious other problems that plague this engine constantly. H0e said that he would not have another CAT engine. He says that the Cummins engines are easier to find places to work on it and part and labor seem to be cheaper as well.
The only input I can give is that I have driven coaches with 8 airbags and with 4 airbags. Both were very good. Even a good well balanced coach can be a nightmare to drive if not properly loaded however. If the coach drives well empty, the rest is up to you, just be sure you take a good long road test over a variety of road conditions.
I have a cummins in my Airbuss and no probs as of now it still has alot of power and,,, yes the parts are easy to find (I work for Cummins,, but that's the other story)
I hope u have an engine brake on your's