That engine was made as both an inline 6 and a V6, i.e. the 6T71 and the 6V71. I think the 6T71 (the earliest model) is the one best known, but both were widely used. The old Detroits are 2-stroke diesels, a unique type that require some specialized mechanic knowledge. For that reason, some people avoid them in favor of the Cat and Cummins e4-stroke engines. Lippy says they are easy to work on, though, and I have no reason to disbelieve him.
Any old coach is a potential money pit, and diesel engines are particular ones due to the high cost of things like injector pumps. If you aren't a do-it-yourself mechanic, 12v electrician, plumber and appliance repair guy, you probably ought to avoid any old motorhome. But if you enjoy tinkering these oldies can be a lot of fun.