A few things to consider in addition to the other responses. Remember that even fairly late model Allis tractors did not have true "live" pto like your Oliver does. If you wanted to change gears, you pushed in the clutch and the transmission was still coupled to the PTO. Hence, the tractor could be pushed and it was almost impossible to change gears until the mower spun down. This is why the put in overrunning clutches.
Your Oliver is totally different. You can clutch, change gears, do whatever with the transmission and it's basically 100% decoupled from the PTO hence eliminating the need for an overrunning clutch.
In addition, even when shutting off the implement, the PTO on your 1855 includes a wet type fiber brake of a single plate design. This brake can handle a reasonable amount of slipping associated with stopping a high inertial load. We have a 720 Woods and there I've had no issue applying the brake with the mower going full tile. That said, the best method is to shut off the PTO wait for it to spin down a bit, then engage the brake.
Moral of the story, that overrunning clutch is unneeded with an Oliver and is just another liability.