Ok, apparently there are none in captivity that someone could measure.
But I found a bracket and gear box that I can buy and have shipped across the country. $150 plus freight. But that would leave me looking for a mule drive, which would also have me buying in the east and shipping west. Then the belts.
Right now I'm leaning toward building the bracket based on "best guess" measurements and mounting a spare 14HP motor on the tiller until the auxiliary hydraulic system is installed.