I remember black-faced impala being mixed in a different exhibit. I wanna say it was the Beisa and a gazelle species. The Giant Eland used to be closer to the Skyfari, mixed with Marabou Stork. I'm sure over the years things shuffled around though.
I think it was @Giant Eland who told me about the Eastern giant elands mixed with Black-faced impalas on Horn & Hoof Mesa, or at least he posted about it somewhere in the forum.