Not that difficult but is time consuming to do a careful job. Mainesail has a play by play of his position sensor on his site
Installing A Raymarine Rudder Position Sensor Photo Gallery by Maine Sailing at pbase.com which is about how I did it. I had the gyro put in the computer, in for a nickel, in for a dime . . . .
Photos show my radial drive wheel before install, and the mount block parts I made to install. Part for ball joint on radial drive wheel is aluminum. (Ooops, sailnet doesn't seem to like my photos and I can't spend all night on this. Resized under their limit, but that didn't work)