That is one hell of a niche! Seem to remember Boddington hunting in Greece where rifles (like, all of them) were prohibited whereupon he used a slug gun.

I'm under the impression that the OP is not necessarily a "globetrotting hunter" but would simply like to return to Africa. If that's the case I think he'll be fine with standard stuff.

Bore size is no substitute for shot placement and
Power is no substitute for bullet performance. 458WIN