RE: Differential
I considered differential when building my last 424 Q-500.
I ended up not installing differential on my high wing model.
For everyday racing there is no issue in turns or general flying.
When not racing the rolls are barrel shaped instead of axial. That is what you will see on a high wing racer without differential.
Installing differential to the ailerons is relatively easy:
1) Use a round control horn on top of your aileron servo.
2) Drill a hole for the aileron push rod approximately 20 degrees in front (toward the engine) of the normal aileron holes.
3) Use Z-bends to connect the aileron push rods to the servo.
4) Connect to the aileron normally.
When testing the differential there should be more up aileron than down.