The model D was made for years & years, in several configurations. Most I see are pto drive, but they all have the stub shaft in back for belt drive. I've seen 2 I think that had the pully on & no pto drive up front. I believe if you found the parts, it would be easy to convert between the options.
They also had a direct engine drive (I never even looked, I imagine through a clutch on the pto drive shaft?) that would mount on a truck bed, for those that did custom shelling.
There were also several types of clean grain chute from the vertical elevator. I've seen just an angled chute; a chain driven cross auger up top; and the best, a v-belt driven swivel cross auger up top. (No slip clutch on this puppy - in a dew, we stripped the bevel gear on ours...)