I know for the Tempest/LeMans, the front bumper is different between the two years; not sure about the GTO's, but probably the same. Of course, the front valence is different too.
Then there's the side-marker lights, the vent windows . . . you're just going to end up with a clone that's not even right, and everyone's gonna identify your car as that lame attempt at a clone.
Why not just personalize the car yourself? Or make it a Q-ship with poverty caps and a 350HO?