I had a slowpoke with an OS .25 spinning a 3 bladed prop, 8 by something. What a great little airplane. I agree, balsa ought to work. But, if you are really worried about the strength, laminate a couple of pieces of 1/8" strip or throw in a strip of carbon fiber. Depending on the weight of the balsa, 1/4" can be pretty delicate, whereas two 1/8" strips CA together can be surprisingly strong. If you don't think your hinges will go deeper then the plans show, carbon fiber will make that stab really strong. Just have to work out the thickness of the fiber.
Trailing edge
Carbon Fiber
Balsa strip.
Fun airplane, well the .25 slow poke. Especially if you can find some trexel tires. Just seems to fit the cartoonish lines of the airplanes a la clancy lazy bee,