Hi Erik,
that Nile Lechwe would be from a game ranch in the US I guess? There are so few left in Ethiopia now, so I don't know if they can be hunted in the wild. As for the stronghold in South Sudan... things aren't going to well there, even though there must be some fantastic hunting areas there.
Jerome, thanks for the confirmation on the forest buffalo from Gabon; looked at the picture and agree with you, they do seem to have horns that go straight back (I guess so they can get through the thick forest without hanging up on branches)...
Spike.T and Jerome, that other old photo; I'm with you on the waterbuck. However I can spot a very long lechwe-like horn in the background... hence why it's a shame there isn't more specific info on where it's from. I also wouldn't rule out Kob... native to NE Congo. There must be antelopes there that disappeared before we even really knew about them; I know of two. Robert's Lechwe from along the Luapula in DRC/Zambia, and the Upemba Lechwe (of which at the last count there were 4 left...).