1/2 ton, 3/4 ton, yada yada yada. I know a guy that works at a spring shop. He has told me in the past there are differences in 1/2, & 3/4 ton spring rates. The same width, length, and thickness spring can have a different spring rate depending on the amount of iron used to make the steel, the way it was heat treated, the speed of the cool down after making it, the amount it was arched etc. If you go to a spring shop they could build you a set of correct length springs at the 3/4 ton spring rate, and correct number of leaves. If you want an extra 2, 3, or more inches they can do that too with more arched springs not blocks or stacking up extra springs.