David:
The skid steer adapter could work, if we welded a PT plate to it, or I am sure one of our more creative types could weld up a similar gadget.
As I recall, one of the many adapters Mark Chalkley got for his EarthForce had three point connections, and he hunted around and bought a 640 RPM hydraulic motor with spline shaft. I don't know whether he's put them together. I think the hydraulic motor was marketed as PTO replacement.
It's certainly something to think about, since there are a lot of cheap 3 point implements, new and used, that might be adapted.