I've seen just about every mod you can think of on a GT/CS, including putting it up on a 4x4 chassis!!
I wouldn't especially say no to doing anything that can be bolted or screwed on to any Mustang. It can be undone in a matter of minutes. If painting your fenders pink makes you happy, go for it. It's your car!
However--I disagree with MCA's comments--only by the "quick to judge" tone. Give this BigBob guy a break. I'm guessing that Big Bob is new to this, and that he isn't up to speed with what he has. He wrote this board asking for help and direction. We have no knowledge if he's a "Mustanger", or not. Don't knock him for wanting to put a horse and grille in there.
BigBob should know that the reason there is no horse and corral on the GT/CS (HCS) grille is because it's supposed to "look like a Shelby GT". ('67-70) Shelbys have no horse emblems. It's empty. The GT/CS has no horse and bars fender emblems, too (but one is on the pop-off gas cap).
Making your GT/CS look like it used to gives it a lot more interest, and the authenticity not only adds value, but in today's world of jelly-bean cars and an SUV at every turn, it WILL stand out as a unique Mustang by showing the world how it used to look--today!
This website will help you see just what you have. Jon has done a great job here.
There are other members here who can "guide" you to a direction to a restored looking GT/CS.
It's important to understand not to judge people without knowing what they may or may not know. As much as I know and have written about these cars (2 books, now out of print), I still say to do what makes you happy. Life is too short to live and do by other's (elitist) standards to do a car perfectly that you can't drive and enjoy--just to satisfy three days of the year at concours car shows.
I can guide anyone into knowing every square inch of a GT/CS; every nut and bolt; how to restore and impress the strictist of judges (even MCA judges). But...the bottom line is enjoyment, not obsession.
By the way...when I bought MY GT/CS in 1974, I bolted a Mustang II chrome grille horse into the original grille. By 1978, the Mustang craze started, and horse was IMMEDIATELY tossed!!
The rest is history....430,000 miles later.
Paul.