Your seats require the metal seatbacks due to the single mounting tab at the top. The plastic backs use two tabs one on each outer corner. The plastic backs will not interchange with your seats without modification to your backs. Attached is a picture of a pair of 68 Firebird seat backs showing the two mounting tabs. These are the same for all mid-67 thru 70 F-bodies, and mid-67 thru 69 Corvairs. The repro plastic seatbacks are marginal at best, but when you have nothing they are better than what you have. I know of one interior manufacturer that has been working hard to duplicate them exactly as original but it will be a long time before they ever make it into production...............RatPack....................