Ideally you would get longer springs, and longer shock absorbers to go with them. Readily available for trucks, of course, but not so common in this case.
At some point, you would be beyond your camber adjustment range. Not sure if you could get 4 inches or not without modified control arms or control arm mounting points.
Taller tires has potential, though your speedometer would not be accurate, and at some point your gearing would be higher.
Perhaps you could "augment" the fattest spring pads a couple of inches with a truck part that is often called a "budget boost" pad, or "BB" for short. 2 inches is typical on these. I can imagine one designed to fit some trucks that could probably be fit onto your MB with minimal modification. You would not get any extra travel, but you might net around 3 inches of extra height over stock with this combination. Not sure on the camber, as I mentioned, though at 65kph on dirt, would you even notice?
Now if you did this, the downward travel would be shortened. It is unlikely you could get longer shocks for it (maybe, who knows?). However, it might be possible to fashion a 2 inch (or more) spacer block to bring down the strut mounts accordingly. Downward travel is useful on rough roads.
Perhaps a combination of some suspension lift and somewhat taller tires would give you the clearance you are looking for.
Best of luck!
1986 300E 5-Speed 240k mi.