Well, I finally got the center block back from the Career Center, where the students made it for me. It took a while, but I can't complain about the price -- it was free!
I had a smaller scale rig similar to the one Thomas posted a pic of, using my 1 meter (3 foot) blade from the Cadet mounted to the bucket of my Kubota. It worked well enough, but it was very far out in front of the tractor and difficult to control precisely. I broke a weld on it (one of my poor ones) by hitting a large rock and just remounted it on the Cadet. The main reason I moved it is that the Cadet has only a manual lift for the blade, and sitting on the tractor while trying to steer, run the hydro lever, and raise and lower the blade irritated my back problems and often required a third hand.
I hope to get a chance to do some more work on this project this weekend, and if so will post some pictures of the progress.
I am a little concerned about the relative rigidity of this thing. Is it possible to limit the downward motion of the loader arms but still let them float upward? If I can do that somehow, then angling the blade downward will permit it to simply slide over objects that it doesn't move aside.