I HAVE A 79 MALIBU WITH A 12 BOLT OUT OF A 67 CHEVELLE WITH LADDER BARS AND COIL OVERS AND I CAN RUN 4.5 BACKSPACING ON 28X10.5 WITHOUT ANY FRAME NOTCHING.BUT IF YOU HAVE A 7.5 YOU CAN ONLY RUN A 3.5 BACKSPACING, ANYTHING MORE YOU WILL HAVE TO NOTCH YOUR FRAME