The car has had a few changes from the beginning but as far as I can see, the shape of the bumper has not changed. They have a few with no actual factory grille, just a wire mesh screen. THey may have even used a fiberglass replacement front bumper.Look closely at the bumper.
Compare the actual movie car with another 70.
It's different than a standard 70 bumper.
...and all sorts of die casts have been produced in the time since that movie came out...
...with that hideous bumper.
Post up some side by side pictures...I can't see any difference.