True, the Firebird rear seats should be the same for coupe and for convertible. So they may have had experience with Camaro's which will have a different seat width from Coupe to Convertible.

But Firebirds should be the same. So if it's indeed a Firebird seat, you should be fine. Now as to Standard and deluxe, I believe the main differences are in the padding and in the covers... as in thicker padding so a slightly larger cover in size to accommodate... but not positive on that.

Brett - 67 Drop Top 455!