I just had a close look at my 83' 126 and the front plate is just very slightly bent in the middle. However my front bumper has a recessed area for the plate to sit in which I don't seem to notice in your picture. I presume the difference is that mine is Euro-spec.

As a consequence, the plate does blend in somewhat with the bumper curvature.

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1983 w126 280SE - daily drive
1983 w123 200 - sold