In my truck dodge there is a 1" block raising the back end. That can be flipped to the top of the axle to lower the bed 1". It does not change the spring rate but does lessen the available travel. I had it that way for a while but when hauling large weights the axle would hit the rubber. That truck might have 4 to 6" blocks that could be removed or swapped out for shorter ones. Front springs might be special or might have blocks too (just guessing on the front).

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.