Bumper Guards

Here's my dummy question of the day: I see photos of all configurations -no bumper guards front or rear, fronts only, color keyed rears only. What determines the configuration? Years ago in FL it was a weakly enforced safety regulation to be equipped with bumper guards. The 6 or 8 prev. Mustangs I had, had them (all '67's & '68's). My current CS (from L.A.) has front & rear. Any documented guidelines?
Neil

Here is a thread that will help explain

http://californiaspecial.com/forums/showthread.php?t=3393&highlight=bumper+guards

How confusing! My first Mustang (a '68 Coupe) bought from the original owner had F & R bumper guards. It was a later model '68 model as evidenced by the rear fender reflectors. It was an east coast built car, not San Jose. The dates of the factory build changes apparently have no real bearing.