I picked up a set of 2013 factory cummins wheels cheap the other day I'm wondering if they will fit on my 89 w250 ?

 

Same bolt pattern (8x6.5) but might have different backspacing. Look on the back of the new wheels. They'll have the wheel's size and backspacing cast into them. Should read something like "18x8x25". "25" is your backspace in millimeters.