Why diesel?
Most class C's in that size range will be based on Ford E-series chassis, or the Chevy equivalent, with a gas engine. A diesel generally implies either a Sprinter chassis (usually a little smaller as it's a bit lighter chassis), a Ford Transist chassis with optional engine (smaller/lighter still), a Promaster chassis (very much smaller and lighter), or a super-C based on a heavier duty truck (usually larger and considerably more expensive).
If by a "free-standing dinette" you mean a table and separate chairs, that's pretty rare on a class C, though on some it would not be too terribly difficult to replace the existing built-in dinette with something more to your liking. Some do hide systems stuff in the dinette base, which would be problematic for such a conversion.
King size beds are also relatively rare. Queens or short queens are more common. Having a long bed in the back is somewhat difficult because it forces a long overhang to provide walking room around the bed aft of the wheel wells. There are some alternatives with "sideways" beds in slides that might be practical for a king sized bed, but offhand I'm not aware of any that actually have one.
On the whole, I almost get the feeling you're looking for large class A diesel pusher sorts of arrangements in a class C, and that's simply unlikely to happen. Maybe I'm misjudging that.
