A four inch drop is going to have to reconfigure a lot more than just suspension. Brake lines, drive lines will need to be shortened. Shocks will need to be resized for the shorter suspension travel. How much space between the axle and the rubber stops anyways? If it's, say, 6 inches and you just lowered the rear 4 of them, you are left with 2 inches of travel.
In order to balance the front, you'll have to lower it as well, affecting some steering components. Think this option all the way through before going forward.