In the article of Magnum,June 1996 issue, that picture is seen with a comment: "Selous with his Gibbs-Farquharson (as yet unrepaired with sideplates)."
BTW, another article dealing with Selous`s Gibbs rifle can be read in "The African Sporting Gazette", issue number four. There You can read that Don Heath from Harare owns a Gibbs Farquharson rifle that possibly was once owned and used by Selous. Unfortunately all records of Gibbs have been destroyed during WW2 but there are several indications that Selous might have owned this rifle or at least ordered it.

Kalunga