this is exactly what i was looking into, however, i know GT mustangs come stock with 245/45r17s in the rear, and the tire isnt all that small. i wasnt sure rather or not it would fit into the wheel well or not.

 

depends on the offset of the wheel, but it'll fit most likely.

 

Wheel size and offset depends on how "jdm" you want to be = how much camber you want to run.

Here's what I like and I know it works:
front: 17x8 or 17x8.5 +25 with a 225-235 series tire
rear: 17x9 or 17x9.5 +35 with a 245-255 series tire

This is pretty flush, imho, and doesn't require crazy negative camber.

Be wary of wheel spoke design if you have Z brakes. Also, you will probably need to remove the plastic fender liners and roll/cut the fender lip to prevent rubbing.

 

uh, there isn't a specific one. you can use what ever you want to. i have 25 on the front of mine and 42 on the back (but i have 9" wide wheels and I'm running a 275) but you can get away with 25 all the way around. or even 0 all the way around depending on your wheel you chose.