Hello Alec and welcome to the group.
Your question is a very difficult one to answer, but as Achim suggested, a query to the Classic Centre Archives in Germany might help.
These cars were imported as complete cars to South Africa and not as knock down kits for assembly at the East London plant like many other models of the time.
Also, you need to take into account that quite a few cars were imported privately into South Africa by owners, hence the few LHD cars floating around here. Mine is just such an example.
You can also direct a query to the East London plant itself (the Museum on site to be exact) and try to speak to a gentleman by the name of Norman Hickel.
There is also another gentleman that runs a sort of informal register for the W113's here in South Africa. Last time I discussed this very issue with him there was about 50 pagodas that he knows of. Again, the problem is that not many W113 owners here belong to the Mercedes-Benz club of South Africa or the informal registry.
So, there may be many more than 50 pagodas floating around here...