Nate,
According to Meredith, who isn't always 100% correct, the 1969 Model year began with production started on 1 October 1968; this would be with chassis number [113.044.xx.5585] where earlier is a '68 and this number and later is a '69. The xx is 10 for standard, and 12 for automatic transmissions, I believe.
Headrests I can't be as sure about; I'm pretty sure they were standard on most '69 US spec versions, and maybe even some late '68's. However, it might be a moot point: Today, in restoration, it is not uncommon to add them. I've seen it done with a '66 230SL, as well as with an early 280SL. So the presence or absence of headrests can't be a definitive gauge of age.
As for radios, MB's of this era ONLY had Beckers installed at the factory; Blaupunkts were lower cost and higher margin US dealer installed options. Since radios are very easy to add or subtract with their DIN dash mounting, many cars have gone through quite a few radios in their lives, perhaps from none, to a Blaupunkt, to an 8-track, to a cassette, to a CD, and back to a "correct" Becker when the car is deemed a collectable and is pampered and or restored. Would not surprise me if that kind of thing happened in the nearly 40 years of existence!
The model and serial number of the Becker--regardless of model--can be tracked with Harmon Becker in New Jersey. They'll tell you when the unit was made...contact Ed Ebel, search for his info on this site.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored
