Hi Steve!
Yeah, I could have. At that time, I'd owned a Cub Cadet for about two days, and couldn't tell a QL from an SG, narrow frame, or original... and I still haven't figured out how to identify which ones used which muffler bearings, what blinker-fluid to use...
But I did have machine tools handy. Somewhere in that period, Keith showed me his fleet... his Briggs Vanguard driveline used a 1" diameter SGT shaft, (according to my torque and whip calcs wasn't necessary) but it solved coupling problems in his arrangement. My spare parts pile wasn't well stocked, so I used what I had available. Life's more of a challenge at 3AM!
One of the biggest reasons why I went to the U-joint in the rear was because the fan diameter wasn't much bigger than the rag joint that was ~2" away. Not very efficient. By swapping it out with the u-joint, about 3/4ths of the rag-joint's shrouding disappears, so airflow over the hydro improves. The hydro may, or may not be such a thermal problem, but either way, mine runs cooler now.