Overrunning clutches are nice but rarely necessary for someone who is familiar with the tractor. On rental units or if you have people working for you who only occasionaly operate the tractor, the clutch prevents the implement inertia from pushing the tractor along unexpectedly. But other ways to deal with it are to slip the pto lever into neutral, or simply avoid driving up to an obstacle with the implement turning at full speed. At the worst, even a 6' or larger rotary cutter only pushes the tractor along a few feet. Once you are accustomed to how the system acts you may not care about getting an overrunning clutch. There are about a zillion tractors without them.
As akways, prompt cheerful refund if info is bogus. Dick B