I am going to be upgrading from the stock 9" rotors we both have stock on our vehicles (like the 4 cylinders of all years). You will need new struts because i've heard that there the holes to the spindle line up different, you will also need the spindles for the 11 inch rotors because otherwise you can't mount up the calipers. Good luck!
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'84 Mustang 5.0 LX
My car