Rutger,
it is a bit difficult to answer your question since I do not remember what car you have. Is it a 280SL RHD?
{Why not adding this information to your signature line?}In any case this radio is a "mutt", that is, it has the knobs of an early 'small-face' radio but all the type/model markings - the label on the left side (looking from the front) and the bar in the front - are gone, making it difficult to figure out what it is exactly, but most likely it is a later standard DIN radio. In addition the chrome is pitted, thus all in all not an attractive radio.
The answer to your specific question however is that it should fit - IF you have a 280SL LHD car because the body of the radio should go through the regular DIN sized opening in the dash. My guess is that a RHD 280SL is not different. Measure the radio opening in your car and then you know - the standard DIN opening is 180 mm x 55 mm.
I remember that you do NOT want a stereo radio, but what else is important to you? Does FM have to go beyond 106 MHz? If not then take a look at: eBay 261461161867, or 261458967653, or 171306152443
If you want the extended FM range go for eBay 310940539154 (even if it has 6 buttons and thus is a bit after 1970)!
Plenty of choices.