We installed a set on our 92 Gt. Rear springs sat around 1/2 inch lower from stock and the front springs had to be cut one coil to sit level with rear.
I have the airbag, but i haven't used it. It was on the car when i bought it and i'm most likely swapping out the springs soon in favor of a suspension set-up geared towards handling. I will say that they transfer weight very nicely, back sits down quickly when you get on it.