Here's something you don't see everyday. Brett has had this for a while and plans on restoring it. The trencher is driven by a separate engine. Here's a quote from him that he sent with the picture.
"It is a Jeep-A-Trench made by Auburn gear I think. I talked to one guy and he said he has never seen one on a FC before. Several years ago when I bought it I thought it was an airplane tug till I started digging through the brush and realized what it really was. I cleaned the rat nest out of it and everything turns. I put The arm together the way I thought it should go. I farted with the engine for about an hour before I put the project on the back burner where it still is. There is also an extra chain for it too. The guy I bought it from said he used it to run water lines on his Ranch. It's pretty cool . You can drive the truck and run the trencher at the same time by walking beside the rear driver side. It has 4.11 gears the spring packs are about 10 inches thick all original. It had a mount for a blade in front but one didn't come with it when I bought it."