[Captainfab]

The '71-'72 12 bolt will be a direct bolt in but will be 1.5" wider that the rear end you have now. The '73-'87 will also be 63.5" wide, but will require the spring pads and shock mounts be cut off, and the trailing arm mounts and a panhard bar mount welded on. All of these will have the 5x5 wheel stud pattern. If you can find a rear end out of a '68-'72 Chevelle/Malibu/El Camino, those will be aprox. 1" narrower than your current differential, and have the 5 x 4.75" wheel stud pattern. But you will need to perform the same cutting and welding on those.