Back to the original question for a second: John, I think you may have read that the visble ones on the bottom had washers, and the top ones were just a large slotted screw. I recall hearing that -- and lo and behold that is how my 63 is. Can't guarantee mine is the original set up though -- but no reason to think otherwise.
I can't imagine why only the lower screws would have washers.
When I bought my '65 230sl, the grille had a few washers only, incompletely scattered in both upper and lower locations. I always thought some previous owner had misplaced the rest of the washers.
The washers are necessary to ensure the screws always go in vertically and prevent damage to the grille shell (very thin metal there).
I currently have stainless steel screws and washers of the $0.15 local hardware store variety, and these shall remain until I get around to replacing with chrome equivalents.