Australia seems to be infested with this craze for lowering W111 and W108's'
I could rant for hours on the folly of lowering a W108 which does nothing for the handling .
The height is set by measuring the angle of the lower control arms to the ground surface . A rule of thumb is to set the chrome trim on the rocker so that it passes through the centre of the hub caps.
I am on the road at the moment but I have the standard factory spring lists at home .I can repost them here if you need them.