Really for the W123 which appeared in 1975?
I'd rather think it was a proposal for the /8 series (W114/W115) which appeared in 1968.
I tried to check it out thoroughly and found the following on the Pagoda SL website, which I thought would be fairly authoritative:
QUOTE
Submitted for your greater enjoyment:
My work with the living legend himself, Mr. Paul Bracq has given me unbelievable experiences and a wealth of information for which I feel very fortunate. Speaking with Mr. Bracq is a joy as he is so enthusiastic about everything! Many of you know the MBCA-International Stars is nominating him for inclusion in the Automotive Hall of Fame, and that's how I've come to know him.
Did you know there was, on the drawing board, a W123 4-door Pagoda? Drawn in 1962. Take a look:
Download Attachment: W123 Pagoda.jpg
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Check out that Pagoda roof; but look at that wrap-around glass at the C pillar! Whooeee!
UNQUOTE
Was Mr Bracq wrong then?