The trick to using a B body rear is that you move the springs in, the B body rear sits right on top of them, and with no other mods, and you can put 13" wide tires under there. If anything other than this was done you the rear, then you have to figure out what rim back space and tire sizes will fit on a case by case basis. BTW, 65-67 B body rears will require less back space than similar 68-70 b body rears. All of this is explained through out the forum, and if your still confused, there is plenty of help here to sort it all out.
