The widebodies (77W) are for LHR - JNB service. Overwater ETOPS is not required. 120min is sufficient for over Africa operations. Sunair had some 77W slots reservered, I wonder if its not these. The narrow bodies are to replace frames that have gone to Mango.
EDIT : PS-> SAA did have 7 x 772s on order years ago. Cancelled them when Coleman left... (ZS-SCA to ZS - SCG)