Are you able to take some pictures and post them? Does the servo work at all before mounting it to the chassis? There many types of servo horns that a person can buy and use. Some RCs put the ball stud on top of the servo horn, and some times the servo horns are taller than others; placing a ball stud on the back side is called for in some instances. It all depends on the steering's design and servo placement. If using the Amp's stock servo horn on the new servo, it should be pretty much a direct swap I would think.