Your ride height should be about the same with a different axle, within an inch. You can reuse your existing springs. You just have to remount the spring perches on your new axle to match up w/ the leaf springs.
I have super large spring packs since mine is a 3/4 ton, about 11" thick. When I replace my rear axle, I am going to remove some of the springs to lower my rear. I have a heavy duty truck shop around the corner from me that specializes in springs. Im going to talk to them about making me a new front set with hopefully only 2 or 3 leaves in it to lower my front.
