Rocky--
you can make 9in. rims fit by doing whats called a poor mans mini tub. Very very simple. This will allow you to run a 17x9 with 5 inch back spacing. To go any larger than this you have to remove the leaf springs ie coil-over suspension. here is link for poor man mini tub;
http://www.mustangdepot.com/graphics/pm-mini-tub.pdf
Dan-