This event appears on the FIA Calendar (published in the 1970 'Yellow Book') as the Pietermaritzburg 3 Hours. Status is International, with classes for Sports Prototypes (Group 6), Sports (Group 5), Grand Touring (Groups 3/4) and Touring (Groups 1/2). Organising club: Maritzburg Motor Cycle and Car Club.
However, as it was part of the Springbok Series, it appears to have been subject to at least one local rule, which limited sports cars to 2 litres in 1970. The classes on Racing Sports Cars appear to be wrong, since Group 3, which they lump in with 1 and 2, was for standard GTs and Group 4 (there with Group 5) was for modified GTs, which are unlikely to have been matched against pure racers. Here's how Martin Krejci describes the series:
Until 1963 the Springbok series was destined for F1 cars before it switched to mixed sports car and touring car field. The main race of the series was well known Kyalami 9 Hours, which enjoyed good international competition. Also many of the other races were well supported. Sports cars were limited to two litres in 1970 but three litre cars were still allowed in the main 9 hour event, so even factory Ferrari took the challenge and won in Kyalami three consecutive times during 1970-72 period facing opposition of Porsche 917 and other great machinery of the time.
I believe the classes should read as follows:
A: G1/2 up to 1600cc
B: G1/2 up to 2000cc
C: G1/2 over 2000cc
D: G3/4 up to 1600cc
E: G3/4 up to 2000cc
F: G3/4 over 2000cc
G: G5/6 up to 1600cc
H: G5/6 up to 2000cc
In practice, I doubt any of the saloons or GTs were unmodified Group 1 or Group 3 cars and as far as I can tell all the entries were homologated to run in Group 2 and Group 4 - including those rotary Mazdas! I'm not familiar with the Bramhill (presumably a local special) - that might be the reason Group 7 is mentioned: although why would anyone build a small one-off single-seater sports car?