Ron (clubpro) can get you the valance & exhaust tips (PM him).
The valance is not welded anywhere. Remove backup lites, license plate lite, rear bumper guards (if so equipped),rear bumper. There are 2 fasteners (1 on ea side) in the trunk well that secure the valance on each end, then 6 or 8 screws along the top edge of the valance.
A word of caution: I did this mod on my C/S, and the repro valances have a tendency for poor fit. The one I got was about 3/4" too short, and the contours @ the ends did not match the contour of the rear quarters. I ended up taking my original valance to a body shop and had them cut out the repro's exhaust cutouts and splicing them onto my original valance, and repaint. Then everything fit well, but at an extra expense of $300+/-.
I had the exhaust shop have the tips extend 1.5" from the valance (measured at the top edge of the tip to the valance)
Neil