I did this on my 420SEL and it was a piece of cake. The headlight wipers actaully folded out of the way. Then from inside loosedn the big round thing securing the turn signal and slide it out far enough to get some working room. Be careful with the tabs holding the old headlight door on as they get brittle and and can break. I used a butter knife to gently pry the old ones off. The bottom was the hardest part but I just got down on the ground and went to work. The new ones just pop right on, slide the turn signal back in and tighten it up, close the hood and that's it.
1995 E420 - retired
1986 420SEL - retired