I think your best bet then would be to contact the MB Classic Center. They'll be able to answer your W124 measuring questions.
Currently going through the same thing on the 107. On the 107 this is done by measuring the vertical distance between the center line of the lower control arm bolts and bottom of the ball joint on the earlier 107's or a measuring point just inside the ball joint on the later 107's. The back is pretty much the same procedure. it is adjusted by changing spring shims and or springs. Essentially you are measuring and adjusting the control arm angles.
Excellent description, Roncallo!
The current factory method is using a Romess Inclinometer, inputted into SDS.
I don't think the 107 or 124 has the appropriate pads to install the Romess Inclinometer?
They have two real axle shafts and two front lower control arms . . .
I was looking at a video of how the Romess Inclinometer works for the Mercedes. It appears there are pads to place the inclinometer on for the newer cars. But the 107 has no such pads and no good flat section on the lower control arm to place an inclinometer. It would seam to me you could use it with some kind of adapter but there is data in the 107 manual of what the inclination of the front control arm is supposed to be or what the rear axels should be. There fore it seams to me the only way to do it would be to set one up correctly with the original tools and then measure those values. But I'm still on step one, setting up with the original tools so I can get those angles.