Since this can be very dangerous I'll tell you how I do it.
On 190SL's I put a jack under the control arm and raise the arm up until I can fit the king pin together.
This car is different and you will have to undo the four screws that hold the lower control arm to the sub frame. This would be the inner portion.
Place the spring in the control arm and fit to other end it into the sub frame. If there are any rubber bushings use some masking tape to hold them in place so they don't move or fall out while you are setting it up.
You will need to place your jack about half way down the lenght of the control arm so that it will move up towards the four holes in the sub frame. This may take several attemps to get the holes, jack and lower control arm to move in the right way. Once you get it up near the sub frame you might be lucky enough to get a long drift to go through the holes in the sub frame and lower control arm so that it will all line up.
At this point you will have a lot of tension on the spring so keep ypour hands well clear of everything as you work. I've also used a piece of threaded rod to go through the holes and then simply used a nut on the rod to pull it all into place.
Regardless of how you do it, it has to be done this way or you will never get it together. In other words, the upper control arm, upper pivot, king pin, lower pivot and lower control arm all have to be assembled first, then you install the spring last.