It should work. I bought a set of Vogtland lowering springs to install on my
1995 E300D. I have not yet install it as weather is too cold to work on it.
I spoke to Eibach about it and they don't want to confirm it. Our diesel car
is lighter than 300E so it is not a weight problem. W124 chassis all uses
the same springs... except for coupe or cabriolet which has stiffer spring
in the rear.
With 20% stiffer spring rate, I think it will be fine. Be sure to replace
your spring pad... I'd go with thicker one for better dampening.