Here is the layout of the autopilot.  It is simple in the extreme.  The linear motion of the autohelm is translated to the rudders by just a block of wood with a pin in it sliding on a Formica strip covered wood; rails are not necessary.  The end of the block lifts slightly under load, but this does not appear to affect the responsiveness nor sensitivity of the control effort.  We have been using this system for 12 years now, and have found it only necessary to tighten the lines occasionally, which can be done in the fly.

This is a movie showing how the Autopilot works.  Boat speed at the time was about 10 knots.   The movie is in Quicktime format and is 4 meg, it will take a bit time to download, not recommended if your ISP is slow.