[colton]

You need to get the complete rear axle out of the same generation of mustangs which has a B series number. These are the limited slip units. Now more then likely these will be a five lug unit, so get the rest of the part needed for the front, or check into how to make it into a four lug rear end. The reason I suggest this method is because to just put a LS diff in the present housing might prove to be more expensive to do and it may not stand up to what you are very long.