Pedro, Hitec 645 servos are overkill with 107 ounce torque for this size of aircraft with a 63" wing span. The Futaba 3003 with 44- 57ounce torque will suffice for all flight controls. The 3003 is also much lighter in weight than the 645 and cost less than the 645. The lighter the better for this size of Spitfire, also the Hitec 82mg servo is ideal for the retract air valve, that's what I have for the air valve too.
http://mnbigbirds.com/Servo%20Torque%20Caculator.htm
Roger
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