I actually attempted to place a GT grille in my V6, but I wouldn't recommend it. As mentioned before you must cut the two clips off the GT grille (good luck with resale). Not only this, but the GT grille is larger around the bottom so a lot of stress is placed on the headlights when installed.
Here are the steps I had to go through:
1. Install wiring harness and switch (a kit intended for the mustang will have this; it will look better and you will not have to guess).
2. Remove old grille (easy step).
3. Install new grille. I had to melt and sand off excess plastic on the bottom of the new grille, but if you are not careful you can sand off too much. Once it is sanded it takes an unbelievable amount of time, muscle, and patience to get the grille in place (two man project) and even when complete, it will not be flush at the bottom (two inch overhang). I drove around worrying about it popping out all of the time, so I just replaced it with a grille and foglights intended for the V6 and it looks so much nicer.
4. Connect the fog lights
If it is all you have and is a temporary thing and you don't mind a little overhang (you can't notice it unless you are looking for it) then go for it. But again, I strongly recommend a gt to v6 conversion kit.

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Stabled for the winter...
Black with Grabber Orange and Pony Side Stripes, Fog Lights and Black Chrome Grille, Tinted Windows, Black Turn Signal Housings, Smoked Exterior Light Covers, 18" Black Chrome Deep Dish Wheels with Chrome Spinners, Triple Gauge Pillar Pod with Gauges, 12" Sony Subwoofer and Amplifier, 8" Shorty Antenna, ZEX Nitrous Kit, ZEX Race/Purge Kit.