IIRC you have a Mag 18 in this tractor and not the Onan so that will make a difference.
I've heard good things from these people so maybe check with them.
http://www.ebay.com/itm/Replaces-War...MAAOSwl9BWG9We
I'm not sure how the 6" pto's mount to the M18 engine. I think your 4.6" bolts to the front and the one I listed uses a torque bracket so that needs to be checked too.
Here is the newer style but I bet it's the smaller size. Maybe they can make it for you.
http://www.ebay.com/itm/CUB-CADET-68...EAAOSwYHxWH9Ap