Clicker,
I have asked a few questions and it is about 1/2 day to change it as there are significant rigging checks to be done. I have discussed this with a very experienced current P-51 engineer who says that he thinks that now most operators use the high gearing (15 deg aileron deflection) so I was wrong about the structural loads being a problem (that came from another engineer many moons ago). He thinks that the only reason now why someone might use the medium gearing (12 deg aileron angle) would be if it proved difficult to rig the ailerons so as to maintain cleaarance between the ailerons and the wing skins when set at 15 deg.