There is no "Tri horn"... it is just the standard control surface horn that is supplied.

You install one on the underside of the top wing, and on top of the lower wing, then connect the two via a pushrod, so that the one lower wing servo effectively drives both control surfaces.

This is NOT the optimal way of doing it on bi-planes, but after comparing the "proper" technique against this much easier installation in flight, I see little difference on this size plane.

The "proper" technique would involve cutting the control surface and installing a specially made horn ( something YOU must fabricate ) so that the interconnecting pushrods are connected at the trailing edge of the control surface. This moves both surfaces an almost exactly equal amount when deflected by the servos.

It works great but I do not recommend doing this for people with little ARF experience.

A 1.20 two stroke will more than adecuately OVERPOWER the plane. The plane was designed for a 1.20 FOUR STROKE engine.

Your 1.20 two stroke will be the equivalent of installing a 1.60-1.80 four stroke in terms of power.

Since the two stroker spins faster than a four stroker, consider choosing a prop of a diameter on the higher end of the range recommended props for your engine, and going with a lower pitch... I'd say a 6 pitch prop will be fine and I'd even consider a 4W pattern prop to let you slow the plane down for landings.