It does matter but not as much as you think. If the shocks are behind the axle the rears will need to be either 110### or 130. Track use only 110#, street may require 130# for compression control to keep from bottoming out. Mine weighs 1520# on the rear. I measured the unsprung weight. Dana, old school American 200S, M/T 10.5wx31, Will-wood. Then 1/2 of the Koni aluminum coil overs and ladder bars. That weight was 330#. My springs are compressed 3.5" at ride height with driver. So 130x3.5"=455#/side. 455x2=910. 1520-330 (unsprung)=1190. That being said I'm surprised there is a 280# (1190/910) difference with the shocks only 4" behind the axle. Obviously the calculation doesn't match reality

Doug