I am running Firestone Firehawks on both my cars. P225 75R 14's on the GT/CS. The 67 Fastback P295 50 15 inch on the back and P235 60 14's on the front, but he wheel opens are cut way open and it is on the deck. I used to run the T/A's and they looked good, but the Firestones seem to ride better and are definitely more sticky on dry roads than T/A’s.
With me the trick is to get the tires under the fender without the car to high. Personally I like my cars lower than stock.
I think the back fit of wheels is first thing to consider. Stock wheels are not “dished and allow a bigger tire without rubbing. I like the Torque Thrust and American Racing wheels in the 15 or 16 inch. The Shelby ten spoke like on Arlie’s car is a great choice and is also very flat with most of the wheel back. Crager’s are offset out and in the “over the counter not special ordered wheel” and can cause problems.The Magnum 500 is another good choice.
Stay away from 14 inch rims. Very few tire selections in that small a rim anymore. I have them on my GT/CS and they will go soon.
I think your first decision is to decide if you want a custom look via custom wheels. Then select that and tires are kinda a matter of preference. I do not like white walls on a Mustang, but that is me. I like raised white letters if it is a known performance premium tire (T/A's, Firestone, Goodyear) and not some cheapo brand. I have the black sides out on my White GT/CS and rasied white lettters out on the black Fastback.
Rob