Maybe someone with a 1977 Firebird Assembly Manual could weigh in. Stripe and decal placement dimensions should be in there. I forget where I got my '74 hardcopy version but maybe you could search for a downloadable version?
The black is sprayed over the existing colour. It is not gloss, has its own code so it has a similar satin sheen as the vinyl decals on it for a custom #19 mix. The measurements are in the service manual, as are the paints, although exact mix details and codes not terribly of useful these days. That other respray pic is somewhat custom in details and has 79 door decals.
Many repaints are wrong. That's fine if they wanted a custom touch, not everyone wants to copy factory every time, especially the hurried masking and measuring by guess. Another thing that is common is incorrect door decals or correct decals used on the wrong doors so they lean backwards and don't match the door shape. The 79-81 spoiler front decals and mirrors stripes are not correct but look neat. Again, this is sometimes the owner wanting to customise to their own taste, but more often than not it's just a lack of attention to detail or knowing what was correct to start with, and those that sell the kits provide incorrect information and details so can't always blame the owners.