Hello Hugh,
First off, very nice original motor. Hopefully your plan is to keep it original and not restore it, as nice original examples like yours are harder to come by as time marches on.
As far as the reversing feature it is pretty simple. In my experience There are several pieces that make up this assembly, however there are two key pieces ( clamp dog & ratchet ) that when not maintained or used correctly will cause this feature to fail. When you turn the tiller handle from forward to reverse the ratchet releases the clamp dog allowing the lower unit to rotate in a clockwise direction engaging into the reverse position. Rotate the tiller back to the forward position the ratchet releases the clamp dog again allowing the lower unit to continue to rotate in a clockwise direction engaging back into the forward position. If it has not been abused you should be able to work it through its motions by hand. ( while the motor is not running ) in all a full 360 degee rotation. It was designed to function with the motor running on the boat in the water. It will most likely not function while running on a stand. Once you get the motor running and if the reversing feature is functional. The lower unit will need to be adjust to the transom height if not the lower unit could strike the transom while shifting it from forward to reverse and back to forward again.
Any further questions feel free to call me.
Respectfully
