The system lordmeren pictures in the above post will work very well and give the same results as a staight run would give. The problem might be in making sure the lines do not jump off the pulleys if there is a lot of positive Ackerman. I often use guides to route the cables around obstructions resulting in different lengths with no problems. There is also no problems having different length between the horns on the moving surface being different that the length of the arms on the servo as long as, at extreme throw, no binding occurs. What is important is that the length of the horns on each side of the moving surface be equal and that the arms on the servo be equal.