Years and Years ago I had the sales brochure for that M&W mower and M&W 9-speed over/under-drive for the '61 to '63 Cub Cadets. Both items were on the same 4 page Brochure.
Guy that owns/runs I.H. Cub Cadet.com said the other day He had an offer of $7500 for the last 9-speed He had. The 9-speed only fit the early CC's, not sure even with lots of custom machining if you could get one to work on a model 70/100 or newer gear drive. I've got four Cub Cadets now, don't want a 5th one, especially an original. We had one from 1963 to 1965. It was still mowing a sorta small city lot last Dad knew about 15-18 years ago. IH dealer repainted it red/white when we traded it in on a 70 so it was easy to spot. The 70 is out in my shop, got a fresh rebuilt 10 hp Kohler and new paint.
I wonder if the Cub Cadet in your pictures used to belong to Bill Deturk? He was the expert on those M&W 9-speeds and frt mounted mowers.