just to recap the last post - it isn't just the width of the tread, but having enough wheel to plant the tread in an effective way. You move the springs in and then the limiting factor is the wheel well... if you move the wheel well into the frame rail that's the most there is without surgery to replace the whole frame (back half). Except for the tires themselves (drag radials???) that's life with a 67-76 hardtop Dart.
