You would have to remove the 9C1 springs when replacing them. Why pay for replacements when you can cut the originals. I cut 3/4 of a coil of the top of the springs in my 9C1 and it dropped my car to the same ride height as an 'SS, which is about 27 1/2" from the garage floor to the highest part of the wheelwell molding.
Keep in mind that my 9C1 only has about 68,000 miles on it, and I also lowered the rear of the car using small spring compressors (NAPA $5 each side). Each car will be slightly different.
Use a cut-off wheel with a die grinder or a sawzall with a carbon blade for cutting metal. I used a torch (not supposed to) to cut the springs. Before cutting I placed 2 vicegrip pliers on each side of the cut, that I had placed in the freezer for about 4 hours before cutting. They acted as a heat sink and kept the spring from over-heating.
If you can do the labor yourself, this way of lowering your car will cost you almost nothing.
Email me if you have more questions.