Anything dated 1967 is certainly not a prototye of a W113. We all know the W113 design was pretty much set by 1963 and in production in 1964.
It looks very much like a modernization exercise, perhaps with elements that would later appear in the R107.
Mr. Bracq sent me many photos over the years of design exercises that he did for the W113 in 1960-1962. I posted one before (and again here, the color one dated 1960), and here is another. I should note that the Engelen book barely, if at all, gives mention to Paul Bracq. I should also mention it is one of the ONLY books about SL's that does not mention him. What I posted below is unsigned (but in M. Bracq's collection) because it is part of a technical illustration. The color renderings are indeed signed and dated. It appears as if the more technical illustrations--those in B&W such as the one posted below, are never signed and are generally part of a several view technical illustrations. They are often followed by a color rendering and those are signed and dated.
I mentioned once before that I have copies of patents for the Pagoda hard top, naming Bela Barenyi and Paul Bracq as co-inventors. One might think that a co-inventor would get a little more credit. I can't read German but I suspect the Engelen book isn't perfect or complete.
Now HERE is a prototype [drawing only of course] of the W113...circa 1960 or so. Can you see the resemblance to the 190SL? It should not be a surprise; Bracq did the V.2 hard top for the 190SL and guess what THIS hard top looks like?
N.B. Knockoffs with "gangsta" white walls...I love it!