More in-depth information on the Jeep-A-Trench can be found on the CJ-3B Page: http://www.film.queensu.ca/CJ3B/Literature/JeepATrench.html
The below information is courtesy of Keith Engel, proud owner of an original Jeep-A Trench.
I have a 52 3A (listed on your site) which has some parts that others may find interesting. I have found these parts to be fairly rare. My 3A spent it's life as a trencher on our family farm in Iowa. When I last wrote I was tearing it down for a rebuild. It is now going back together and I am doing the body work. Most of it is in primer now and I hope to have it done for spring time driving. But, back to the interesting parts:
The attached photos are of the drive train parts for the first generation Auburn Jeep-A-Trench attachment on my farm Jeep. As you can see in the photos, the hand brake drum is removed and a large ring gear takes it's place. A bronze cast "sleeve" attaches over the tail of the PTO and this has attachment points for a smaller gear. An engagement handle that is under the drivers side of the jeep is used to extend the small gear into contact with the large gear. This drives a PTO shaft out to the rear of the Jeep to power the trencher in relation to drive shaft speed. Thus, you can have two PTO shafts running at different speeds to the rear, plus the drive shaft. A remote clutch handle is also attached to the clutch bell crank so that the Jeep can be "driven" from the drivers rear corner, from outside the jeep. I have retained all of these parts and they are now painted bright red to show off the uniqueness of the mechanics on this piece of Jeep Equipment History. I hope other Jeep fanatics will find this as cool as I did. There is also a factory Steering wheel lock that bolts to the windshield frame. When I have that reassembled, I will send you a pic. My plans are to keep the equipment in place and modify it ever so slightly. The steering wheel lock will become and "anti theft" device by adding a padlock to it. I am doing fabrication to add a piece to the large ring gear to serve as a "parking lock" because the trencher set up removed the parking brake. It will only be useable when at a complete stop, but a pawl will engage the large ring gear when complete that will lock the rear drive shaft when engaged. As I complete the project I will send more pics, or feel free to request any others you feel will go well on your site. A few other items of note, the trencher package had coil spring overloads in addition to the leaf spring packs, and the tires were 7.50x16 instead of the 6.00x16. there was also a dual rear wheel set up. Last was what appears to be a dealer installed aftermarket heater, other than the normal Harrison Heater."