i know this is a fairly old thread, i have 1,500 pound coil helpers on my 4x and the best thing about them is when im empty they dont tough the frame. rides stock empty, has a 3/4 ton suspention when loaded. i did have to knock off the ears on the factory lift block that served as bump stops (used a torch) heres a couple of pics:
ive also found a way to do this with a taurus, bolted a pipe between the lower control arms to act as a axle housing, used a pipe coupler to act as a bearing and for the coil u-bolt to clamp to, used a conduit clamp to secure to top of the coil to the body of the car. my rear strut springs were weak and now it has a muscle car stance, the coil helpers are about 30 bucks at autozone. the car does ride stiffer but having good headlight aim at dark has been worth it.
and the truck with a overly-tounge heavy load of oak firewood.