Steve - the threads on the other end of the crank are indeed for a pulley. It's that little cup pulley on all IH Cub Cadets. Install the cup pulley next to the flywheel, then the washer and then the nut to hold everything on.That long crank has threads on the one end for a pulley. I’ll bet that is the service motor crank
Ken is still building a mini bike...and that would be cool, but a 122 will be better.
122 mower PTO will need the long shaft if it is 1" diameter x 2-3/4"-3" long (I forget the exact length needed) on the end missing from the other cranks.