Well, my recollection is that Kruger is fenced, yes. But that side of Engonyameni is river bordered.
As to Engonyameni, and other areas of South Africa, yes, they are pretty much all enclosed at the perimeter, by fence or natural boundary. When someone speaks of "high fence hunting", most of us think "Game Ranch" wherein the lions are in 60 fenced acres of Area D and Eland in 200 fenced acres of Area B. That is hardly the hunting experience you'll have at most first class hunting ranches in RSA.
BTW, 45-70 appears to be legal for Cape Buff in South Africa as FF points out. Same for Zim, apparently. The only requirements appear to be a minimum .375 Caliber with no mention of Muzzle Energy.
However I truly appreciate the lesson re Tanz. I'd no idea that the 45-70 reached only to 93.4% of the Tanz minimum Energy Requirement (Buffalo Bore). I'll be using the 50 AK in Zim this year, regardless.