I am not familiar with your tractor & its age. Back in the old days, prior to PTO shields being tubular riding on bearings on the shafts, they were covers over the top half that slid over the top and attached to a slot in the shield over the tractor PTO shaft. The slot is similar to what I remember having on our old tractors (meaning like Farmall H & M). The shield on the implement had a latch mechanism that that fit in the slot and locked but I can't see anything in your picture that stirs a memory of the latching mechanism. That could be because my dad and uncle got rid of the shielding as being too cumbersome. Fortunately my only injury reminder of missing PTO shields is a large scar on my right thumb, not a missing limb like so many.