Another thing or two. With a 4" drop in the rear you will need an adjustable panhard bar. You will also probably need shock relocation brackets for the rear, I don't recall how they're set up. I know on the 67-72 series the shock angle is too steep when stock, it gets worse with lowering. Gas shocks are a great improvement, too. You should be able to get all of this where you get the springs.
