The first question is why are you not using the rack Heidt's recomends for your application. ? ? If you go to Heidt's web page and down load their catalog, Near the back of the book they have several pages of Engineering info about the Mustang II design. moving the rack up-down fore and Aft will affect bump steer and ackerman angles. Other ford pieces can be used when the width is changed . another source for info is Welder Series. They build weld it yourself hot rod components and their catalog has a lot of good installation information.