Look at my post in "Old pictures of our SLs"
One picture shows a W113 with aftermarket alloy wheels. They are "BBS" style. There were many aftermarket manufacturers in Germany offering alloy wheels for the SL in the late 60s, early 70s.
The factory "Bundt" wheels were made by Fuchs and were forged. They carry a MB part-number. The same design was offered in cast alloy by companies like Intra, Ronal, Rial and others.