Hello: I have a 56' Olds 88 and am interested in putting a 57' Olds Rear End in it (for posi-traction). Can anyone say if it has the same distance between the leaf spring mounts and the wheel face-to-face distance as the 56'? Also, what about a 58', 59', 60' or 61' rear end, would any of these work? I'm hoping that someone out there with more knowledge on this subject can help me. Thanks. James