The return to zero spring was located at SS is a little tricky. The cross member xx was slotted on the bottom to allow two stop posts to come up from the base. I suggest you look at ThrustMaster's to see how they implemented a coil spring with straight legs straight in conjunction with the stops. I had access to aluminum, shears and break. I'm sure one could make this out of wood also.
Shilded cable is recommended to reduce stray noise pick-up.
A Y connector can be made to plug into the computer to pass the main signals to the joys stick and pick up the rudder cable. I don't have more complete plans. Hope this helps.