My personal opinion is these 3d planes beg to be powered by high torque 4 stroke engines. I would think you would be better off with a Saito 100 and 16x4W prop at the very least and the most you would need would be the YS 110. If you watch the weight you can keep it to under 7 1/2 lbs. The Saito 100 would fly that pretty good. With the YS you can mount the tank over the CG for better balance and you get a bit more horsepower. I personally think the OS 160 is a bit too much for this plane. I had one on a H9 Ultra Stick Lite and it flew it nice. In fact I really liked the engine, good milage and a lot of power. But the power is better suited for high speed not high torque. For that reason I'd stay with a 4 stroker on the Mayhem, or similar 3D planes.
Thanks,
Barry