I agree. I mostly build rock crawlers but am working on a 1956 3600 build as well. Ideally you should cycle the suspension and measure full compression and full extension. However, at ride height I generally give 60% of the shock travel to compression and 40% to extension. In the rear application of a truck I would think this would be even more crucial as the ride height is generally a bit higher in the rear to account for loading of the bed or a trailer.