Hi Tony,
I did much the same job on my '82 380SL a few months ago, due to the left lower control arm mounts breaking off the sub-frame.
Yes, the left wheel actually folded under the car!
There is a recall for this problem on cast iron engined cars, but apparently when they went to the aluminum engines MB decided the problem would go away.
Guess what, it is still there!
Be SURE to have a REAL GOOD look at the lower control arm mounting tabs.
They aren't very strong, the sub-frame was designed for a lighter car with a smaller engine.
Originally used on the 114 chassis vehicles.
If you find any signs of cracking on the mounts, sub-frame and/or around the mounting tabs (They have the slots in them for adjusting the lower control arms in or out) you should replace the sub-frame!
You almost have the sub-frame out of the car anyway.
I was able to exchange the sub-frame and replace all the mounts in about 4 hours of labor-intensive work.
It was actually easier to replace the engine mounts with the sub-frame out on the bench.
I installed a good used 114 sub-frame, which I welded the MB sub-frame stiffener kit metal pieces onto.
The car is much quieter with the new engine mounts and sub-frame bushings installed.
While you are in there have a look at the steering coupler also, it is a part that will eventually need replaced.
Also, if you have any slack in the steering gear you may be able to adjust it easier with the sub-frame out of the way (provided you do remove the sub-frame).

__________________
Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C