Discovered I had been operating under a misconception about aileron travel. I had got the idea the ailerons travel 20 degrees up and down, but this spec does not appear ANYWHERE, the only reference to 20 degrees is the movement of the CS128 bellcrank! The POH indicates the ailerons should travel between 1.8-2.4" deflection, up and down, measured between the inboard tip of the aileron and the wing trailing edge.
I had another look at my wing, and confirmed that at zero deflection both bellcranks are at 90 degrees. My stopbolt accurately stops CS128 at 20 degrees up Aileron, and this yeilds 2.2" deflection. The Aileron balance weight contacts the cove at 2.8" down deflection, and this has taken CS128 way past 20 degrees, so it will be stopped by the left Wing stop bolt.