Steve knows his stuff.
Pontiac really tried to breakout the Firebird from the Camaro early on. The 67-68 models shared many of the same parts between them, the 69 Camaro and Firebird only shared door panels and trunk lids, and the 70-up Firebird and Camaro were very different from each other. One of the problems in restoring a Firebird is that the Camaro restoration vendors decided about 15 years ago that they could market to Firebird owners by simply changing their description(s) to say "Fits Camaro/Firebird". Over the years, as more and more Firebirds were restored, owners simply went with what was cheap and convenient, what was in the catalog, and Firebird restorations became inundated with reproduction Camaro parts. And now, all these years later, some of those cars are getting re-restored, and due to aging and weathering, it's tough to know what's original and what's an older reproduction Camaro part.
As Steve stated, you can make nearly any 70-up part fit your 70 Trans Am, but for a good resto, the afficiandos will know which parts are from incorrect years, which parts are resto parts, and which parts are Camaro parts. I learn more everyday about the subtle differences between the Camaro and the Firebird. The 1969's are sort of a nightmare to restore, because they a one-year only body and interior.