I found some info on this. I was mistaken, you can't just take out the front shims, you have to replace them with thinner ones.
They have an explanation here if you are curious:
1984-1996 Suspension Lowering Kit, 12 Piece Car Set From Mid America Motorworks
The ad says you can lower up to an inch, but it doesn't look like there are an inch of parts stacked on the front leaf shim assembly.
The explanation of Mid America's kit is mostly BS.
Here's the straight story.
The amount of factory shims was to compensate for differences in spring rate consistency. Back then, the makers of the leaf springs could not be as consistent as was necessary to have consistent ride heights so GM developed this shim system for C4. The springs which were a little under the specified spring rate got shimmed a lot. The ones which were right on got shimmed a little and the ones which were a bit high got no shims.
In the front, you can remove all of the long aluminum shims. In fact, from the factory, there will be either no shims, one shim or two shims per side. In the rear, you can move all the shims on each spring mount from the top to the bottom of the spring but all the shims must remain. Do that and your car will be as low as the factory would build them.
As for lowering the car more than just removing shims, in the front, you can do that with the wedges most of those kits include. And in the rear you can do it with the longer spring bolts.
But...regardless of what ads for suspension products say, for a street driven C4, any lowering beyond the removing (front) or changing location of (rear) shims will excessively decrease ride travel. With a base car this can have the suspension hitting the bump stops in normal driving situations, especially if you have two people in the car. That decreases ride quality, obviously. As for the "improvment" in handing because you lower the CG, in theory that's true, but in practice on a street car, especially a car with base suspension, the actual improvement in handing will be small and difficult to perceive.
Now, on a car with Z51, because of that car's stiffer springs, you may not be on the bump stops as much, but, again, when you decrease ride travel an inch, you risk hitting bump stops more often, espeically in the rear.
For racing or very aggresive street driving on smoother surfaces, lowering a car with Z51 or Z07, along with suspension alignment for track use will usually make an improvement in at-limit handing.
I realize that one of the big reasons for lowering a car is appearance and not ride or handing and, for that purpose, those lowering kits sold by Mid America and others, are good choices. If you install them...just remember when you give up ride travel, the suspension will hit the bumps stops more often and when that happens ride and handling are degraded.
Lastly, when you lower the car, regardless of why your doing it, you must get the suspension realigned.
