Looked up the Seyfried article, it appears my recollection was not entirely accurate. Not wrong though: once I thought I was wrong but I was mistaken.

"The Great Chobe Chicken Hunt" was actually published in "Blackpowder Hunting" magazine in the fall of 2004. The Selous connection comes from the fact that Seyfried spent the first half of the article quoting verbatim, in full!, Selous' published ostrich hunt with a Gibbs Farquharson, and also the example taken to Africa to replicate that hunt 120 years later was a .461 Gibbs Metford Farquharson with, wait for it, Selous sideplates!

So not actually one of Selous' rifles unfortunately. Worth a read though if you are a gun-mag hoarder.