bulldog -- I wasn't sure how to answer this, so Billy answered it for me and asked that I post the following for him as he lost his internet connection:
Though a lot of people dont believe that putting a spacer on top of a coil creates a 'pre-load' scenario, it actually does. Hence the reason that revtek's rear spacer measures 2" even and gives 2.5"+ of lift, and daystar's measures 1.5" but gives an even 2" of lift. Putting a coil spacer into the rear suspension is not going to render the results gained in the front due to the IFS vs. the solid axle rear end, but the overall theory is still similar. By putting the rear spacer on top of the coil you are essentially moving the upper mount of the coil down the measured amount of the spacer. Obviously this is going to push down on the axle, or up on the frame depending how you look at it, but it also does cause the coil to compress some and tighen up. Though not an exact 'preload' scenario, the coil still wants to fight back in a sense and therefore does add to the lift generated by the coil spacer, rendering the overall lift height to be exponentially greater depending on the height of the coil spacer. Info about this can be found all over the net and is debated relentlessly. It is a tough concept to grasp and I cannot say that I even have a completely confident understanding of it myself, though I hope this explaination helps to shed some light on the situation.
