Hi Mark,
I agree with you it seams logical to me that the shroud can be found on cars that have been equiped with air conditioning since maximum air flow due to overheating was required to be directed to the radiator. If the shroud was added when a/c was added to the car or at the factory I dont know. My car was assembled and shipped to the US in December 1968 and is a 280SL, it had a/c (was removed) and does have the shroud.
Changes that have been made to the 280 SL have been documented in Pagoda Notes Issues 11-1 Page 1 to 8, Issue 11-2 Pages 1 to 7, and 11-3 Pages 1 to 6 also later in Pagoda World Issue 25 Pages 15 to 19. The only change I found that was opening the gap between the fan (called "hub" in German), and the shroud (see my screen shot attached below).
Last month I prepared Indexes that can be alphabeticly sortable (see the General Discussion Forum area), and information can easaly be found using the indexe's.
From the attachement and the only item I found pertaining to the shroud (hub), I assume that the shrould must have been inplace on 280 SL when a/c was part of the order from the factory.
Mark I realize you may not have PW Issue 25 (unless it was mailed to you with our welcoming letter). However, you do have full access to Pagoda Notes here in our Technical Manual. Should you wish to get PW Issue 25 there are back issues that can be ordered.
See here----->
https://www.sl113.org/forums/index.php?topic=11537.0Dieter