I took a look @ a stock GT, still sitting on a lot actually, and the measurements came out to about 6 1/2" @ the front of the rocker effects and 7 1/4" in the rear. These were recoreded at the lowest points at the underside of the rocker panel.
My Sportline dropped clearances are 3 7/8" in the front and 4 1/2".
This equals out to a 2 5/8" up front and 2 3/4" out back. Of course these are estimates of what the real drop is but its safe to say that its not much less. See sig.
-Dan