At this point is seems to be a one-of-a-kind, but it may just be one of those "others haven't come to light yet". Something else to consider is that something like this would mostly be used by businesses, and when they were replaced by newer lifts that they were scrapped.
Green Mfg. Inc. is still in business. I got a PM over on the 'other site' from a fella that had worked there. According to him:
For some reason I am not able to post in the thread you started. But, I find this pretty cool. I was wondering if there are any other markings on the fork lift?? The reason that I ask is because I used to work at Green Manufactoring in Bowling Green OH. To my knowledge, and I worked there for 18 years, we never made a forklift for anything, let alone a garden tractor. But, on the flip side, I can see how Green's name was on it since they produce hydralic cylinders of all shapes and sizes. So I am guessing the Green manufactoring tag is on the hydralic cylinder. Not sure if it was one of our cylinders used in a home made deal, or a vender was using cylinders that was made by Green. Just wanted to provide you with the little knowledge that I have. Good luck!!