The D-100 and D-130 backhoes were actually designed and manufactured by a company called Davis who's main specialty was chain trenching equipment. Creating narrow trenches with an oversize chainsaw was a fast way to get the job done if there were no underground services (sewer,water, hydro, cable, telephone) to get in your way. However, there were also natural obstructions to slow you down such as rocks and tree roots.
That's where the backhoes came in and Davis trenching machines were often sold with one of those hoes on the end of the machine opposite the trencher. Then along came Tenneco/Case and bought Davis lock, stock and toilets because they wanted to add a quality line of trenchers to their ever-growing line of construction equipment. CAT has done the exact same thing.
When Case got into the skid steer loader biz, the D-100 and D-130 hoes were a perfect size for these machines. The added some bolt-on mounting brackets in a spot that did not interfere with the loader. The operator drove up to the hoe with the loader in the air, hooked up the two hydraulic hoses to quik-tach couplers and then mounted the hoe to the skid steer by using the hoes hydraulics to position it. There was a hydraulic stabilizer kit for the rear of the skid steer to make the tractor stick to the ground better.and to level it up.
I'm sure that Case found other applications for them and they may have sold them to other companies that needed a hoe for their tractor. I stared at those crappy photos for some time and I'm not sure just what that crawler is. I have a feeling that it's a 350, which is the smallest track machine that I'm aware Case made. As for the hoe, that did not come new with the crawler because the paint is Desert Sunset. I don't think that it's a 100. If anything, it would be the slightly large 130 hoe.
Oh, one more thing... If that IS a 350 Case, there's no way a 2 ton float would carry it safely, especially with the hoe. A 6 ton tandem would be the minimum..