If I were building that airplane I would set the engine to 2 degrees down and 2 degrees right. The right thrust could be fine tuned according to prop size. Example, for a 40cc twin, a 18x8 prop will require a tad bit less right thrust then a 20x8 ( I think that twin will do either of those props ). Where you will see the biggest gain using right thrust on that airplane is less rudder workload on take off. While on the subject of less workload on takeoff, on gas engines I always extend the throttle arm so that I have a 2:1 ratio between throttle arm and servo arm. This allows you to use full servo travel and then adjust so that the carb opens up to 85% at full stick. That last 15% gives no additional power with these engines. The end results is a much more linear throttle curve and you can lean the high speed needle down just a touch more which will help eliminate the mid range burble common with gas engines.