I am building a truck based on a Model A frame that has been Z'd in the front and rear. I am trying to figure out if I have the amount of 'Z' that I want before I get too much farther into the build. I have a Posies Superslide front and stock '48 Ford rear spring. Can anyone tell me the approximate rates for these springs? I know the weight of the engine and transmission as well as the weight of the body going on the frame, so with the spring rates, I should be able to roughly figure out how much the chassis will settle. I know I can mock it all up, but was just trying to save a little labor.