Marc, one more thing to remember, which a lot of resto shops overlook. Pontiac did not paint the engine compartment all at one time. A lot of resto shops make this mistake. Shooting the entire engine compartment one shade of black is of course easier, but when these cars were rolling down the assembly line, various parts were sourced from different suppliers.

The firewall is indeed 20%-30% gloss, but other components, like the inner fenders, core support, heater box, wiper motor, etc. were all sourced from different suppliers, and they used varying shades of gloss black. In fact, sometimes the level of gloss varied by batch and week produced.

I think just a general guideline of black levels is good for 99% of us. But if the heater box is a slightly different shade of gloss than the inner fenders or wiper motor, don't fret, just let people know that's the way they made them.