Bud, the device you're talking about is a servo reverser, costs about $20.00 at MPI Inc. I have a GP Ryan STA with dual elevator servos which I installed one of these, and it really works great! The real benefit is that by reversing the throw of one servo it allows you to install the rudder servo in the middle of the tray nice and straight using the cable pull-pull system. The elevator servos would then be installed on either side of the rudder servo with the arms towards the inside. To not use the reverser would force you to put the rudder servo at one of the ends of the tray instead of the middle and the cable system would then be at an angle and not straight. Obviously, the elevator servos would be right next to each other cramping things even more! I really think this is the way I'm going! I really want that peace of mind with this airplane!