I would put it in the 122.
Like Jon said, make some attachments. If I had a rear pto, I would look for a woods rm48 mower and make it a pull behind mower. If you turn the driveshaft around so the back is the front, add some trailing wheels to the now back of the deck the existing casters will be in the front. Add a tongue and go.
Turning the deck around should match the deck pto direction to the cub pto direction...unless I got myself turned around trying to figure it out.
Bill