That's one of the reasons I modified my 69 Firebird the way I did. I modeled it after the original Firebird 455 H.O. engineering test car, so there's no right or wrong.
As for what's right or wrong on a 69 Trans Am, if you don't want to be scrutinized by every person at a cruise night, and you don't wish to have people judging your car (whether you want them to or not), and you don't want to invite people to tell you something is "wrong" with your car, then don't try to build your 69 Trans Am (or clone) to concours level quality.
However....at the same time, you can't throw together a clone Trans Am, incorrect colors, wrong stickers, no Ram Air, etc., and get the same respect that a guy would receive that spent years restoring a real 69 Trans Am, to show quality standards and correctness.
As for the red decals, Firebird emblems, etc, read the link below to see how these misconceptions came to be.
And it's your car. If you want to put Camaro emblems on it, hey, whatever floats your boat.
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1959-1980 Pontiac Window Sticker Reproductions : http://www.pontiacwindowstickers.com
My Bio: I am currently writing articles for POCI's Smoke Signals magazine and enjoy promoting and discussing the history of the Pontiac Motor Division.