Gordon,
After reading this lengthy thread it is quite easy to see why so many posts were added, and yes there are points to both sides of the debate. I won't get into discrepencies of the car, but would offer to say that the car appears to be a real RS Z at this point, and it is quite obvious that you have a lot of car there to work with. Since you pulled the trigger on this deal without the required due dilligence most would excercise, I suggest you now lick your wounds and learn to appreciate what you have sitting there.
If I can further caution you on the car, don't rush to remove parts in the quest to find it's authenticity and end up breaking or damaging parts, but get the proper info on where to look and how to get there. Many of the knowledgeable people on this site and others would be happy to converse with you on the car, and can easily show you what to correct should you discover things that are not quite right on the car. Whats important is the fact that 2nd generation cars are well on the move $ wise, and you have a great car to work with should it require some work over the next couple years.
You can always drive it in the summer, and do a partial resto on a budget over the winter without having to redo the entire car at once should that be the thing that makes it right for you. I have owned and inspected many muscle cars over the years, and this one may have stung you a bit, but it's far from the type of car one should bail from just because it's rough around the edges. Fact is, the market is strong, and you will come out of this alright in your pockets. Don't be so hasty to dump it. It's a hot car that's very much in demand.
Tom