My experience with early Fergies, I had a TO20 and a MF 35, is the TO is like it's Ford cousin the N series. Both brands had tranny driven PTOs back then and you needed an overrun clutch on the PTO for both. Even my '63 Ford 2000 which is a blue 600 Ford series (30 hp) has a tranny driven PTO and I have to be careful what I do with it as with it too with a rotary mower I need an overrun for it to work safely.
Put one on for about $75 from TSC new and you will know what I'm talking about. Be sure and match the PTO shafts. In the early days they were 1 1/8" dia input shafts required for the attachment, 1 3/8 for the output as I recall and later on standardized with the 1 3/8 input shaft.
If you have the wrong drive shaft you will either need an overrun with a small input/common out as stated, or buy an additional adapter. I would not recommend that as anything else on the drive train just amounts to more "loose bolts" and more vibration.
Mark