It is going on a Yanmar VIO 27. I also wanted a thumb, but I use my machine for plumbing installlations. The thumb, even folded ,would make it hard to get under footings. It would be that much farther to hand dig. I found it on Ebay. I don't have the name handy but the phone number is 724-694-3390. It is made to fit a quick tach on a Dingo walk behind skid loader. They are going to weld a flat plate on the back not the Dingo mount. It is 27" wide. They make them in several larger sizes. I plan to weld a bracket on the back just like a bucket has. My Yanmar has a hydraulic quick coupler for the bucket. I can change back and forth in just a couple minutes while sitting on my seat. As soon as I get all the materials together to make the mount, I'll post some more pictures.
The best part, it cost the same as a hydraulic thumb.