Fitting the new Mustang II crossmember and welding it in is where one wants to take the most time. Establishing the centerline of the new crossmember, to that of the old straight-axle, can take a bit of time, but it is vital to wheel alignment and position. The inside measurement between the framerails should be 29 inches. Any gaps can be shimmed, in order to achieve the desired distance. After all the measurements are taken the crossmember is tacked into place.