I believe that in an ARF the incidence is pretty well set by the manufacturer, and in sport/sport scale it is less important than it is for competition aerobatic flying. I agree wholeheartedly that the only things that matter are the alignment of the wing/stab/engine. The fuselage simply acts as a means to keep them flying in close formation

In my GP J3 ARF, there is no slop that would allow any deviation from what GP has determined is the optimum wing/stab incidence and the engine thrust line is fixed by the firewall and careful installation of the engine into the engine mounts. Engine mounting is relatively straightforward, so I have concentrated on making sure the wing incidence (washout, or lack thereof) is identical for both left and right wings, making sure the engine is mounted straight in the mounts. and ensuring that the flying surfaces are square in all three axes (lateral, longitudinal and vertical) in accordance with the GP instructions

HTH,

Jim