the 28 inch span Guillows Spitfire... that's going to need to be kept LIGHT or its going to be a brick. Maximum I would do with off the shelf would be 3 channel elevator, ailerons and throttle, and it would be electric power. (a bit hard to throttle control a Cox .020 even with the gizmo that someone sells to do it.)

I'd use a rewound CD spindle motor (size and weight compares well to 3 quarters stacked on each other) and brushless ESC, and 2-cell Lithim batteries. and GWS "Naro" or Tower TS-5 servos. (just 2 servos) GWS's micro 4 ch RX or some other RX that barely covers a postage stamp.

Forget retracts at that scale. they will add too much weight. the retract mechanism an servo make the landing gear 3 times to 5 times as heavy as using wires and wood blocks for fixed gear.

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Since it is a FF model conversion... if the control throws are minimized... it actually can be used as a trainer. It would not be a great one (small and a bit fast for its size). FF models tend to level themselves out if left alone. That is the main idea behind a trainer design... it WANTS to fly straight.