Gotta agree with JD9600guru. All 9x00's were hydros. One goal of gearcase beside engine was to eliminate long belts and drives of the two major power consuming parts of the combine....ground drive and main separator drive. Checked further into Sales Manual for early 9000's, and hydro was standard equipment. There were no factory installed substitutions available on the hydro. Besides parts catalog has no parts breakdown for Posi-torq groung drive. But, early in the development of 9000 series, there might have been some one-of-a-kinds running around.
I didnt say I saw it or knew/cared how it was done. I think the guys a member here so maybe he will chime in
just because it is/isnt on deeres web site doesnt make it gospel.
I spent a lot of time looking for parts to an alternator conversion kit for a 4020 that was built by deere. The website didnt list it, and no parts man had ever seen one....strangely enough not even the guy we bought it from had ever seen one. Mother deeres support network can and WILL fail at times.