They are said to lower the rear 1 inch and level the car.
I bought a set of H&R and used the rear springs only. I bought the H&R because the ride does not suffer, but handles better when needed. They drop the car 7/8 of an inch. This gives the car an ever so slight rake which is what I sought to do. I have pics on page 2 of the talk forum "before and after"
Use the search function and you will find another post. I forgot which one it is.
lowered mine about 1 inch also but didnt like the looks so i put the front ones on.lowered it about 3/4 inch,rides and handles great and didnt change the shocks.
Yes, here is an example of our Roush with GT springs up front and Roush rear springs - measures the same from ground to the center of the fender wheel lip on both ends.