Not sure if different retract units may have been installed but... I have a World Models Mustang 46 that I am just getting ready to fly again. It has a Hitec retract servo for the gear, which is the stock gear. It uses a servo arm with 1" of total throw (each control arm mounted 1/2" out from the servo). I would measure the needed throw for the retract units. I would guess its 1" or very close to it. If not, just divide the throw by half and mount the control arms that far out on the servo arm.