You're correct about 67 & 68 gen 1 Firebirds... No headrest. 69 had an oversized headrest that some people removed in order to have the low back bucket seat. 1970 (gen 2) was last year for Firebird headrest. After that they went to high back bucket seats. I only know this because I have a 70 Firebird, and you tend to learn a lot about the model years on either side of yours when you restore the car. Not that it really matters, just trivial info.