The ball link position is easy to figure out. Plug your rudder servo directly into your receiver so your gyro will not effect the throw.
Move the rudder stick in both directions, with the link disconnected, and determine, by holding the link up to the arm, which hole will give you the correct amount of movement to get full throw in each direction but not bind. (if you get real close but just a hair too much throw you can use end point adjustments in your radio to fine tune)