You won't want anything from 75 to 78 or after about 83/84 when the tail lights changed. The later 6 panel tail lights are larger than those of the gt and you also have trim holes on the later panel which aren't present on the gt.
If you are happy switching to the later tail lights and welding up some trim holes then the later panel will work just fine. It looks as though you have a 6 panel tail light sitting in the boot anyhoo.
