just replace your mufflers with straight pipes, and get an O/R mid-pipe. No more confusion.
Yes, GT stands for Grand Touring, or Turismo in italian, but anyone who would know that, would know a GT from a 6-er anyway. Most people dont know jack about cars, so there is no way you can do anything to impress everybody, other than to buy a very overpriced brand that only makes impressive cars like a lambo or a ferrari. Failing that, you just have to make the car to your own enjoyment. Of course, with a mustang, even if they do think its a V6, they probably think its pretty cool. I like the V6s as well, are you familiar with the Turlingua Mustang? There is something to be said for a lighter engine, and thus lighter overall car. Your not going to be king of the dragstrip without a lot of boost, but... still a great fun car to drive, great track car, and very cool design.