I currently am restoring a 1967 Shelby GT 350, I have been trying to find out the correct rear leaf spring rates, various vendors sell the springs, but do not mention spring rates, they mention 4 leaf, or 4 1/2, they can drop your car 1" etc, I would like to keep my car as stock as possible, the only vendor that I found that said anything about spring rates was "Cobra Automotive" standard spring was 4 1/2 leaf 120 lb, does this sound correct?