Unfortunately there is no real "easy" way to roll your inner fender to make space for wider tires/rims and unless you know what you are doing, you could possibly damage the rear 1/4 panel or inner fender. If this is your first Mustang and you are wanting the dish look for the rear, I would suggest possibly going with a set of our 17" Saleen SC Wheels. They have a slight dish and look killer on any fox body. You could also go with a slightly smaller tire in the rear to help with any clearance issues. Check out this recent blog about SC Wheels on a fox body for more info and similar answers to your questions!
You can remove your quad shocks in favor of our rear control arm kits which will increase the performance of your stock suspension and give you more grip.