Little more..2" or more? The thing is that GM delivered 9C1's with more than one spring height. Fleet sales to PD were with sometimes crazy low prices and quality control suffered. I've seen oem 9C1's measure almost 30" from the high point of the wheel well to the ground; and sometimes 28.7". I've seen that car and the same measurement @ 25.4" after installing Hotchkis or Eibach Pro Kit or Sprint springs, none of which claimed such a drop. An oem Impala SS often was 27.0-27.9 and w/those aftermarket springs be 25.4" - 26.9". or 27.~? It's a crap shoot. The history of all these company is spotted. For a while the now "out of production" Eibach 3832.140 was the best quality control and consistency of installed height of any, and they stopped making it. Who knows why. Helliwig went years with only a small front sway bar, paid to tool up a much better, lighter, hollow and thicker bar...and stopped making it. Capitalism is not an unmixed blessing.
Another funny ... one of my very best handling B-bodies after new lowering springs sat at 27.9 @ the front.