I think Rodd is right. Mine is a later 67 230 and there are no speakers on the kickboard areas.
What you might consider, and it seems reasonable to me, is to use your mono stereo or acquire the Becker TR and ask the guys at Becker America to convert it for you to stereo. They are nice guys, I like calling them and they're very helpful with questions. Their price seems very reasonable for work done, and they told me once they could probably do this, but I didn't follow up with that.
There are also other vintage radio restorers that can convert your radio to a digital one and maintain the vintage look, or so it is billed. I have no experience with this and can not recommend. I prefer to keep things original, like Dr. Benz has suggested in a couple posts elsewhere here, and what that means to me is mono stereo, drum brakes on the rear, no A/C. Keep it a sportscar, but I have decided to install electronic ignition and I am contemplating a mono to stereo conversion of the original smaller Becker radio.
-CD-
1967 230SL, 113.042 10