Precision trunk seal is what 1A use in video. It is the same seal supplied to Classic, OER and similar places. The bags are labelled everywhere about being registered in the US, it is made in Taiwan.....or TW, as it says in tiny letters.
This is the type used, it is not F-body type/size being sold by others, they all seem to fit the same 1/2" channel so swapping around works.
https://catalog.prp.com/images/Websi...1_SA_LGE-2.jpg
This is the listing for Precision 70-81 F body seal.
https://catalog.prp.com/images/Websi...0_SA_LGE-2.jpg
And then many others list either and to suit all models GM. I have the Precision K3020 here, same that is labelled for Classic or OER etc, and is the standard 1" tall type, taller than both of the other versions. So rather than selecting a brand or shop that says it fits your model, you may need to request a particular part number. How tall was stock GM, production era? How easily did it compress, or seal? These seals are probably all fine, in their own application, but if hard to close the lid on these vehicles you generally need a softer version of same, or shorter version in height, or combination of both.
Just to remain confusing, here's another cross-section that claims to be the same thing. 1" tall which is fairly standard and generic. But 3/8" base. What's the channel size on a Firebird? I don't have access to one here. Is it meant to be a snug fit or are the larger sizes perhaps compressed slightly to fit? The K3020 bag I have here is halfway between the 3/8 and 1/2" wide at base, but also tapered as it goes up.
https://www.steelerubber.com/trunk-w...rip-82-0028-84