You're right of course.  I was misled by the name of the large image that RdS posted (300SLRfront.jpg).  The Sromlinienwagen was a streamlined (hence the name) W196 Grand Prix car used for ultra fast circuits like the Avus ring.

The 300SLR was as you decribe but apart from the details (like headlights) they do look remarkably similar.

My comments on the 300SLR in relation to the modern one stand

Michael.