What about the bolts are giving you trouble? Is it just that the pulley turns as you try to turn the bolt? Is this a pulley with 1 bolt on it or many? Is this a car with a serpentine belt or v-belts? I'll admit to knowing nothing about Mustangs, but I know about cars generally and could figure it out by internet.

Also, don't heat them up. There are some pulleys that you need to heat to get off the car, but there should be no need to heat the bolt. If you want to bring the car to Williamsburg I have some good rust penetrator we could try (you won't be able to find it in stores - Wurth Rost Off)