Aren't they just the first edition of the rules that are currently in print by Rattrap/Brigade?
Not quite. The "In Darkest Africa" rules as originally published in
Wargames Illustrated (and found in the Foundry Compendium) aren't the same rules. There are a number of differences: Fixed rather than random movement rates, a motivation system for troops (which I rather liked), different weapons ranges. Clearly "In the Heart of Africa" developed from them, but the official 1st Edition of that game was the one sold by HLBSC and much more closely resembles the game that Brigade and Rattrap now own. The original is recognisably a different game.
Chris Peers wrote loads of articles on DA, I don't recall which exact ones were on the Foundry site. The Foundry Compendium has four articles written by different people, they may be the same ones, I don't know.
They are:
"In Darkest Africa" - overview of the concept and genre, description of troop types (there's no writing credit but I think Chris Peers did this).
"Explorer Chic" - by that nice Mr. Whitehouse.
"Painting Darkest Africa" - painting guide by Mark Copplestone.
"In Darkest Africa" - The original rules and "Snakes and Ladders" map campaign system by Chris Peers, as originally published in WI (again, these
are not the same rules that Brigade/Rattrap now own).