Mudd-ox is the only 6 or 8 wheeler I know that uses a diesel, but I don't think ever used a CVT clutch with the diesel (only gas motor).
I think Argo also offers a diesel in the "industrial model", but I don't think I've ever seen pictures of those that weren't tracked....maybe tracks were an option that everyone bought???
The other diesels you find will be custom builds. The biggest issue is the RPM range. Most will want to run between 1500-2500 rpms. Yanmars will turn a little faster though, and may be an easier motor to tune in.