What are the differences with the Z71s? A friend has a Z71 parts truck with a bad motor. He took the SM465 and that whole assembly for his 88 GMC and I just saw somewhere that Z71s have diffrent spring rate torsion bars. Would it be beneficial to take the Z71 torsion bars and put them in the 90 GMC standard 4x4 I am getting? I know Z71s have different shocks, skiplates, gears, and posi but never knew about torsion bars.