I'm not sure why you would want to do that. I think it would be easy to put a 68 horse and corral on a 66 but not on a 65 since the 65 has bars. The same holds true for 65-66 GT fog lights grilles.
If you want to go that route, then why not get the pony with the stripes that does on the side of the grille. That might look cool, depending on how your car is setup.