There should be no need for a mod to the bolt pattern for the rear bumper. All Contours 95+ shared the same bolt pattern for the rear bumper. Looks is the only thing that changed between the years. The biggest difference is the front end. Other than that all other parts will be a direct bolt on.

96 LX/Sport Roush/ST200 Pro-Flow KKM w/Heatshield Bat Pipe SVT TB,UIM,LIM,Brakes http://www.cardomain.com/id/lxsport