The bottom section (black area) looks just like my 280 SL (1968 assembled in Germany) registered as a 1969 in the US.
It would be helpful to measure the lower outside diameter (I will measure the lower outer circumference later today to see how it compares to yours).
If it is for sale I'll be very interested to purchase it from you.
I have to agree with Alfred, see photo attached from the link Alfred provided your 2nd photo sure looks like the attached photo for the matching / mating assembly area.
Dieter
PS. I am somewhat confused you mentioned in your post you have a 230SL, however, to the left under your user ID and in your Profile you show to have a 280SL 1968. If you have both cars, how does the lower area of your last photo compare to the 280 SL ?