A record set by a Borgward Isabella in 1960 still stands today.
The below snippet is from an informative artcile on the wheels24.co.za site see here for more RECORD TRIP A Borgward Isabella TS still holds the record for the fastest trip from Johannesburg to Cape Town and back. It was set in 1960 (in the days before speed limits) by the legendary oval track racers Boet Ferreira and Buddy Fuller. Their time for the 2900km round trip was 23hrs50min, averaging 122km/h. While faster trips were made after their effort, none can be “officially recognized”, so their record could stand indefinitely. The first image is reproduced from the website and credited to Dirk Engelbrecht and Borgward SA Club.
The below image is from a similar article (in Afrikaans), photo credit as shown: