Ah David ...
This is an easy one.
There are only two blower motor dashboard knobs for the 113 SLs.
One for the early 250ies (until serial no. 002979 and all 230ies), this is the small early window crank-like knob with the flattened edge and with illumination...
and the large one with the blue arrow on for all later 250ies (from serial no. 002980 on and all 280ies) without illumination.
There is definitely no difference between Euro and US model here with the exception that later US models (believe from later 250 SLs on) have the red "defrost" sign around the chrome base of the turn knob. Euro models never had that.
Or ... with other words,
the knob you found in your car is highly non-original for your Euro-280 SL.
Instead, that one is the more simple version of the W110 fintail early version without light.
So, you need to "throw yours away" and get a correct one ...
No offence meant!
Achim