I cut through both panels with a body saw, the cut was thin and was a perfect gap for the butt weld. I had my old quarters cut like yours with about 2" down from the top body line and the same back from the door jamb. I trimmed the new panel and fit it overlapping so that it was about 1/4" below the body line (and same back from jamb) then I put in about 5 sheet metal screws to hold it in place with the screws barely on the edge of the new panel. I started the cutting through both panels about 1/2" below the body lines and after about 8 or nine inches I put a tack weld to mate up the edges and continued cutting and tacking every 4" or so until I reached a screw and then removed the screw and continued on past it. This method left a narrow waste strip of 1/4" wide on the outside of the panel and a wider waste strip on the inside of the trunk which I pulled out later. The waste strip on the inside along the doorjamb I pulled out through the inside of the rear window cavity. The rear of mine at the tailpanel was smashed and rusted badly so I did use the rear portion of the replacement panel and matched it up in the trunk gutter.