Ride height on your car is determined by the coil springs and then fine tuned with the rubber spring pads at the top of the coils. The W124 and the R129 have the same coil diameters, so you could get the stiffer coils from the V-8 400/500E or 500SL and then carefully cold cut to fit. If it's just a minor adjustment, check to see if you're already using the thickest rear pads by counting the "bumps" on the pad skirt.