I'll let someone else explain the Zen-Noh part and the spec differences vs a 2000D. Sometimes I think some guys on here can tell you the names of the workers who built the thing.
I have a 2000BD which is very close to a 2000D. The steering wheel has a greater number of splines than a 2000. The BD has guages instead of lights, I think the radiator housing is the different. The decomp cable is longer on a BD. The side grilles covers the entire side of the engine.
The only real problem I have had is knuckle seals and the alternator which I replaced with a Datsun 510 one for $24.00. The steering wheel I did too mostly for cosmetic reasons. I added a ROPS, which the 2000D ROPS fit with no issues.
As far a price goes, I paid $2500 with a bush hog. I had the charging system to fix though. I assume this isn't a dealer so I'd check the usual stuff carefully.
Jerry