The firewall is not black but painted the same as the lower body color. The balance of the parts you have listed were painted black as noted. The manufacturers did not buy expensive paint for these parts. If I had to choose I would go with gloss black which is what I see on most show cars of the era. Most show cars are way overdone and better than anything the factory could afford to produce. “Better than factory” is not a true factory restoration, in my opinion, but it is what gets you judging points if that is what you are looking for.
There is some paint available from Martin Seynour called REFINISHER’S BLACK, which is the correct sort of smooth but not glossy paint for the inner panels. I usually find it at Napa auto parts stores. The reason that paint is usually gone is that it is about as durable as india ink in that application. The purpose of even painting those parts at the factory was so you didn’t realize that your car wa rusting away right there on the dealer lot. I like the way glossy looks