Positioning isn't critical, but make sure things are symmetric. Also make sure that the bar hits the stops before the pot runs out of movement. Screws through these holes will hold the rudder mount to the baseboard. I have an office chair which has 5 castor wheels on it. Link direcly to 100K linear slider pot by a length of clothes hanger wire.
Springs are rubber bands.
Wooden blocks limit travel. Works reasonably well, though not as good as a commercial device. That could be improved by running the string round pulleys placed directly behind the attachment point to the bar. I had been thinking anout how to do it for a while, and had tried out a slide pot which was unsatisfactory. The pedal I ended up with is like yours except for the pot gearing.