Protecting the S. African complex is a synch, really.
The problem is defending South Africa AND Moscow.
Easier to do then not having units producing in S. Africa.
1) Instead of driving units to Algeria to reclaim Africa, you can start off the bat dumping units into Arkhangelsk on UK 1. That means at least 3 rounds more unit drops in Russia then otherwise.
2) With America going through Africa, America has already saved 40 IPC on Transports AND saved on warships. (2 Destroyers, Battleship, 5 Transports is a pretty good deterant in and of itself, against the Luftwaffe. The Kriegsmarine should be made short order of with the US Air Corps (3 Fighters, Bomber + I like to have two more bombers out of the saved 40 IPC, netting me 10 IPC.))
3) 2 Transports, Carrier, Destroyer, Submarine in SZ 28 (British) + 2 Infantry/Artillery/Armor in S. Africa per round is plenty to stop Germany from even getting the land in the first place, saving cash for England. And once you get 24-30 IPC in equipment in place down in Africa (I like Egypt, close enough to run south if Japan comes close, far enough to run to Caucasus in a hurry if needed) for England and Africa’s yours forever. (Don’t forget, America’s landing 10 Ground Units a round into North Africa as well, it’s not JUST the 24-30 IPC worth of British units there.)