It's not what you want to hear, but I expect it won't fit without some major customization work for the mounting. Unlike generic 3 point implements, the tractor manufacturers sell backhoe and mounting setups designed for their own tractors, not for those of the competition. So neither John Deere nor Kubota are likely to have a mounting kit to install a JD backhoe on a Kubota tractor. That would be sort of like installing a Chevy engine and drivetrain in your Ford... yes it could be made to work, but it won't just bolt right in and you'd have a lot of customizing work involved.
There are several implement companies that make good quality backhoes... Woods, Bush Hog and Bradco come to mind. These outfits make a generic backhoe and then build customized mounting kits (called a subframe) to install it on different makes and models of tractors. If you find one of these backhoes on the market, often you can go back to the manufacturer to get the specific subframe kit to mount it on your tractor.
Just a word of caution about building a "homemade" mounting setup. A backhoe is capable of applying thousands of pounds of force to the ground when it is operating... in multiple directions. And each time that happens, an equivalent opposite force goes back to the tractor through the backhoe subframe mounts. A backhoe/subframe setup that is not thoroughly and precisely engineered to fit a particular tractor can cause damage to the tractor or, even worse, have a structural failure that could be quite dangerous.
Sorry for being so long winded, but I think you need to keep looking for a backhoe... either one from Kubota or one of the third-party brands.
