I believe the back spacing on our stock wheels (2004 or older) is 4.5."
I'm not sure I understand the second question you ask reference "adjusting?"
I may be wrong, but the wider the tire is and the more back spacing you have, the better chance of rubbing on the leaf springs with the inside of the tire.
However, I'm sure someone will chime in and say if you have less of a back space (like 3.5") the wheels will stick out more, but they may rub on the fenders at some point. I guess I'm not sure on that!
Someone correct me if I'm wrong.