Bullitts On Demon..pics!!!

Personally, I'd go with some widened Rallye wheels I'm sure you can grab them for less that $150.00 each new. Might even pick some up cheaper at a mopar swap meet.
If you need a custom offset try here.
http://www.stocktonwheel.com/
The problem with the Mustang rims is it's obvious it's a mustang rim.
It's your car though, so you have to be happy with how it looks, so buy what you like best.
Great looking Demon by the way!