difference in appearance of aftermarket and Nos Fenders... 68 camaro

[justasquid]

So, after much thought, I've come across some NOS fenders for a decent price. But, my question is, How do I tell if they are truly NOS and not just aftermarket ones? Im assuming the NOS will be the correct thickness, and possibly the aftermarket would be thinner? But is there any special features to look out for? such as mounting holes or inner structures?

any help would be greatly appreciated.

[PSV]

I would do a search over at camaros.net, but if I recall the mouting nut for the hood hinge on the fender is a nut tack welded for after market fenders and a threaded hole on gm fenders.