See below for the Align GP780 instructions for the 500. Note the image showing moving the stick left for delay to set the status green; it should be right!
I have to disagree with the comment to use subtrim on the rudder channel. That's not a good idea. For one thing, when you enter setup mode you'll find that the servo will centre to the gyro's idea of center. This will have no relationship to the rudder channel.
I used the 6 star horn. With that you can be sure of hitting 90deg just fine as you get fractionally different alignment if you try each of the six possible positions of the horn on the servo output shaft. From the KX017011T manual, page 21, you'll see that you should set the servo and tail up for fixed geometry; this gyro doesn't need setting up in rate mode. On page 27 you'll find a recommendation to set the ball 10mm out on the servo horn.
Finally note that when setting the limit you should wait for the status LED to flash red before moving onto the next step.