If my old memory is any good, I think you want the spring to be compressed about 35% at rest. Also, depending on how much travel you want I like to have about 1-1.5" of the shaft showing.
Mike
Mike 69 440 Cuda 71 Dart drag car 70 Duster drag car Best et 9.32, 145.9 mph 2019 Ram 2500 4x4