ProRe -
Sorry to hear about the kits, yeah, lousy instructions can ruin a good modeling experience.
OK, enough for the sympathy.
This is were modelling comes in. Instructions can be inadequate or even just plain wrong. It happens, but modeling is more than just good building skills, for some folks. That's were your research and decision making ability comes into play, to make the model YOUR model. In my younder days, I've built a few Mopars, real ones. When I build a model Mopar these days, I rely on my experience with the real thing to get the details right. If my memory gets foggy, which seems to be happening more and more, I have several books on cars of that era, right next to my work bench for ready reference. For my aircraft models, there are always pictures up around the bench for reference, and detail books within reach if I want/need to check on the real thing. Lastly, I may want a fair amount of reality, but it's still MY model, and I can and do take some poetic license when I build and paint. (My last F-16A has detailed marking for an F-16C. Why? The "C" model declas were better than the ones that came with the kit for the A model.)
For you 83 Camaro, do a few google searches, you'll probably find the factroy colors, and can either use Model Master car colors or get the real thing from places like House of Color, IIRC.
AMT does a lot of re-tooling, re-issuing/releasing. So the kit you bought may has easily been released as a race car in a former life. This is usually a good thing, as you get free parts for your parts bin, to use as your research or imagination dictates. Don't feel bad; the F-16 I mentioned, had decals, that matched the box art, but not the instructions, in addition to being, incomplete, and inaccurate, they were too thick to use. The "C" model decals I had were great, and unless someone is checking A/C numbers, don't think anybody will care, I certainly don't!
Archer out.