Wow, lots of stuff going on here. The hydraulic ram shown in post 25 is a push / pull cylinder. Meaning there is no spring return. The ram will move which ever way the fluid is pushed thru the control box on the bulkhead.
The item circled in post 25 is a standard tie rod, a mechanical fastening device which allows slight rotation movement of the hydraulic ram (estimate 10°) , to prevent any binding from misalignment. That nut you circled is a jam nut, which provides no use in your system. It would prevent the threaded ram from unscrewing from the tie rod. Since both items are bolted down, it will never unscrew itself. It helps keep everything tight in the connection.
In order to steer the boat manually with a device (my President has a long manual tiller in the aft cabin - quite decorative actually) you will need to disconnect the hydraulic cylinder from the rudder.
The tie rod is connected to a shiny pin thru the arm, look underneath the arm (and pin) and you can see a cotter pin. Removal of this pin is the best and fastest way to gain manual steering ability. Pull out the pin, slide the shiny dowel up to disconnect the hydraulic ram and now you can steer.
If you are worried about losing steering, I would find or make a manual tiller arm to use. I will take a picture of mine tonight and text it to you. The design is brilliant for a 40 yr old boat.
