Leverguns for dangerous game?

If you want something traditional, the .50 Alaskan in a Marlin 1895 has been used successfully on elephant. Myself I would lean toward a Winchester 1886 or 71 in .50-110 for a bit more case capacity. 500 grain solids at 1900 plus FPS could do some damage. I would give it a go with PH backup.

The best option might be a more modern Browning BLR in .416 Taylor, a proven DG round. In fact, a two barrel takedown BLR with one pipe in .416 and the other in .338 or .300 WIN Mag. could probably do it all for you on safari. A one levergun African battery!