I just started the SG Decathlon last night (I'm reviewing it for RCU Magazine). I am planning to use an OS 70 surpass. The firewall holes in the mount are elongated so they can be spread apart.

2 "Y" cords is all that is needed. In fact, the reason for the extra servo is that they use 2 servos on the elevators. Personally, I think this is overkill. I'll be using 2 servos for the sake of the review, but if I were just building it for myself, I would "Y" the pushrod and use 1 servo.