Lazy Daze offers the Ford 6.0 diesel as an option on all their 26.5 foot models. Others include Big Foot, Born Free, Gulfstream and Jayco. Some even offer a Class C style body on big GM Kodiac diesels - I think the 35 foot Jayco Senaca may be one of those.
There are several Class C's built on diesel-powered, GM pick-up chassis (it's actually what is called a chassis-cab), but the names do not come to mind right away.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL