The hoes that they use on skidloaders attach similar to a backwards 3-pt of sorts. The loaders have a pocket on each side down low for the bottom of the hoe frame to sit in. Now the top end supports, I haven't figured out yet! --- I have seen them laying on the ground, but never on the loader, so I'm not much help on that.
The short wheelbase of the loaders would limit the stability greatly and I assume that's why I never see one in use! Long wheelbase is the way to go if you want a hoe hanging on the back! Front loader helps, but still light on the front. Outriggers only do so much, then over you go!
I have 2 Case 580ck factory tractor/loader/backhoe units and I have had the front ends off the ground when really digging hard! LOL!!
You will just have to decide what amount of use and what digging speed/depth/etc. that you need to do and kind of size your unit from that perspective! It will work and with a little research , something will strike your eye!
Keep us posted on your ideas!

"A machine you build yourself is a vote for a different way of life. There are things you have to earn with your hands."