If I were doing this I would build the engine mount/fuel system/throttle torque rod/servos system as one big working assembly and test it until it worked perfectly. Then I would build the wing around it. The system could be built as a rigid sub-structure comprising two or more spruce rails. These rails would then become the main spars of the wing to which the ribs would be glued. Lastly, you would add the LE, TE and wing tips. I can visualize it in my head easier than I can describe it.