A BH77 is a sub frame attached design and will not fit your tractor. They are purpose built for use on specific makes and models and apparently Kubota never built anything equivalent for your tractor. You also have to remove the 3pt hitch lift arms and linkage to use them.
Your hoe is a universal fit implement designed to mount directly on a standard 3pt hitch. Not as rigid but waaaaay more versatile. And the 3pt lift arms and linkage do not have to be removed and reinstalled when switching between backhoe and other implements.
Dan