Most folks add a small metal arm (generally the little blue aluminum arm that comes with Hitec servos) right on top of the existing arm. The Hitec arm is too short to use for a regular control surface arm but it works great for this purpose. Just remove the bolt that holds the stock arm on, Put the Hitec arm on top of it and bolt it back on. Then I add a small nut/bolt through the existing hole in the stock arm through a new hole in the Hitec arm. See pic.

As to the spring, clip the hook off the end but do not remove the spring.