If it is the rear quarters then you want to weld them on. After some time, the adhesive will dry out and "let go" of the quarter panel. If you are worried about warping the metal just take your time and only do about an inch at a time moving to different spots along the weld so that the metal dont get to hot and warp it. Also you can fill the holes from the clecos with bondo or weld them up. I hope this helps.