I built one quite similar in my Kadet Sr. Used 1 standard servos with an extension arm for enough throw. I used 1/16" music wire bent into a long "V" attached to the arm. I used "Z" bends on the ends connected to the control horns. Works great. Springs open, and springs closed so theres no stress on the servos at all; even when loaded up with a couple lbs. of flour bombs. I operate it with the gear switch on my transmitter.
Have fun.