Syd-Joburg in a twin ..... I'd be very surprised if they could - at least not on the tracks the 744 flies. Probably the same for EZE as well. As an example, you pass about 1800 nm S of Perth flying Westbound, and go up to 64S (some may have flown further South) and over the Polar ice pack. I've seen Heard Island several times (and that is about 58S).
You are a very long way from anywhere.
I'm sure that an ETOPS track exists, but I'd guess it would severely impact the payload, given prevailing winds and weather requirements etc in JNB. Almost certainly, a service via Perth would be a better alternative for a twin.
Rgds
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