I think you're missing a point here....
The rear suspension uses SLS, or hydraulic load leveling, meaning it has no rear shocks in the form that you are thinking. The rear suspension has hydraulic cylinders that are pressurized with a pump driven off the engine. At each of the rear cylinders is a nitrogen "cell", containing a bladder charged with nitrogen. This provides the "spring" in the rear hydraulic cylinders, much like the nitrogen charge does in a standard shock absorber.
Tied into all this is a leveling valve that is attached to the rear sway bar. This monitors ride height and load, and when necessary, either opens or closes to increase or decrease hydraulic pressure in the system. A good example would be if you put a heavy load in the trunk or had a couple of adult passengers in the rear seats - the car would lower from the increased weight, the valve would see this change and open, increasing the hydraulic pressure, thereby raising the level of the car to the point at which the valve would shut off.
"Converting" one of these system to stock shock absorbers never, ever yields results that are equal to or better than the stock system. Period. I'm not terribly familiar with the system on the W124 sedans, but I am very familiar with a similar system utilized on W123 and W124 wagons that works in exactly the same way. People have converted these cars to stock shock absorbers because they (the people) are either ignorant or cheap. They never yield the same ride characteristics, and the car does not perform as intended as it has to be set up for an approximation of a "good ride". Get outside of that range and performance suffers significantly.
Don't take this personally, but you're not smarter than the engineering resources that designed the system. Efforts to "re-engineer" these systems yield marginal, if that, results at best.
Dan
