Is your Wing Derringer from the RCM plan? I really like the look of that plane. You could probably use the Zenoah G-20e engines, but it is a lot more engine than needed.
I would choose to use two Saito four strokes, say FA-91 to FA-125. Not only do they sound much better, you will also save about 1-1.5 lbs of weight (all things included) by using the lighter glow engines.