wire endings at the base are facing in opposite directions, one side will have a greater lift since the coil wire ending will be standing on it's "tippy-toes" while the other side will be standing on it's "heels." This can many times result in a 1/2"+ lean, usually to the passenger side. Many fixes have been devised, but this is one of the simplest, most secure and reliable modifications that you can do yourself.  See the illustrations and description below… Sometimes soft coils can magnify a condition resulting from slightly un-parallel radius arms, thus creating a torsion effect to throw off the ride height from side to side. This can be checked by seeing if the radius arm ends can be evenly moved up and down in each rear mount hole, with the bushings removed, front end on jack stands that and parallel to the body. Several cures could be devised, including "C" bushing alterations as well as slightly bending the radius arms in alignment of each other.

How To Do It...

* Approximately 1.5 degrees per inch of lift is the rate of shim needed under the coil pad in order to achieve close to stock level

2) Take a piece of bar stock, 2.25" wide and 6.5" long, 3/8" thick
    and mill it to the desired angle from edge to edge of the short
    width of the steel. (it'll look like a wide windshield scraper)

3) Cut that piece of barstock in half, so you now have Two   
    2.25"x3.25" pieces

4) Get one of those "contour" gauges (series of wire needles in a
     plastic handle) from the local hardware store for a couple bucks.

5) Lay one of the wedges on the top of the vise jaws long-ways (like
    a long bridge), with just the two opposite edges on the vise jaws.

6) With a ballpeen hammer, pound in the center to 'bow' the wedge
     to the contour of the shape gauge, which you copied from the
     shape of the top of the radius arm (width-wise), where the coil
     cup sets.

7) Make for certain that the bent wedge of steel conforms perfectly
     to the coil base mount on the radius arm. If there is any uneven
     surface conformity, the coil could cause the cup assembly to rock
     or flex in either direction, eventually risking hardware failure.

8) After doing this to both, place them under the appropriate coil
    cup (fat part of the wedge facing forward) and drill the holes
    through the shims. (welding them on to the bottom of the cups at
    this point is a good idea, but not required... well, weld them on

9) The coil retainer ring needs some angled bosses to fit evenly
     under the now 'angled back' bolt heads. Drilling out the threads of
     a 1/2" nut (thin jam nut works great), and then grinding at the
     same angle as you made the shims, will do the job. (Nuts are
     generally  are made hard, tough materials and are small in size)

10) Welding these nuts onto the retainer ring would really be a great
     help when fumbling with the bolts while installing the coils. BE 
     SURE to position them in the correct direction... "the fat end of
     the angled jam nut opposite of the fat end of the shim".

*) Of course you could cut up a typical leaf spring shim from a
     company like Superlift, since they come in 3 and 6 degree
     increments, but the aluminum construction of these shims, under
     a coil cup with an inherent rocking back and forth motion, would
     be a risky choice to attempt. Welding the steel wedge to the
     bottom of the coil cup increases the strength and reliability of the
     entire system. The coil will now be straight, resulting in an even
     side to side ride height and allow for even flex in either direction.