I bought a used Woods 7500 backhoe that was set up for 3 Pt hitch mount. Used it on my NH TC33D a few times - I was aware of possible issues with using a 3 Pt backhoe on most compact tractors, so was really babying it. I finally decided that it was ridiculous to own a backhoe and not be able to operate it properly. Woods had just released their 4 point quick-attach backhoe subframe. They sell slightly different models to fit different tractors. I ordered one of those. The subframe permanently mounts to the tractor, but does not seem to cause much loss of ground clearance. It has 4 mount points on the back of the tractor, two high, and two low. The backhoe was modified by simply unbolting the part designed to mate with the 3 Pt hitch, and bolting on the assembly designed to mate with the subframe.
With a bit of practice, I can mount it in a little over 5 minutes (if I haven't done it in a while, it takes me a bit longer). You back up close to the backhoe, connect the hydraulics (in my case, a PTO hydraulic pump, since I wanted to keep the tractor hydraulics separate from the backhoe's system). Use the backhoe hydraulics to lift it into position, back the tractor in until things engage properly, jockey the backhoe hydraulics a bit to get the holes to line up, place two bolts to lock it in, and you are done. (The box wrench to tighten the bolts rides in a little holster on the backhoe, so you always have it handy.) I do have to remove the upper 3 PT hitch link, but the lower arms stay on the tractor (and are unused). I just have to disconnect the lower arm stabilizers to allow the lower arms to swing out of the way of the backhoe.
If I recall correctly, it did run me about $1000 for the subframe. As an added bonus, the subframe made an excellent place to mount the belly pan I added to protect the underside of the tractor during forestry operations (I'm almost never using the backhoe in my woods, but since the subframe stays with the tractor, this worked out well.)
