The '65 El Camino also has a distinct crease or body line that extends the length of the rear quarter-panels. Plastic filler can hide this line, so place a strip of 3M blue tape just above the top of the crease as a guide. Then sand up from the bottom to this line. Then apply another line of tape on the bottom edge of the line and sand down from the top. This technique will return the body line to the quarter-panel.