A 17x8 +30mm wheel and 245/50R17 tire will be about 1.5" closer to the springs in the rear. My guess is you don't have room for that.
Even worse, the outside of the tire would be about 3/8" further in as well. Probably look really goofy.
So a Mustang wheel is probably not an option for you. They can work well on the front, but I don't see any way to make it work in the back without a 1" or bigger spacer.
Here is a website I like to use to compare. You can put in your current tire and options you find and figure out how the tire would move around based on the wheel.