These were early sculpts by Bob Olley under the Iron Claw sub-brand for Citadel and for 40k Orks, from late 1987 or early 1988. None of them saw general release.
The Roborg was brielfy available in a blister described as IC701 Mekanikal Robot. The tab reads Roborg, which is a better name IMO.
December 1987 / 1988
The Megabot was shown on the Winter 1987 and February 1988 Rogue Trader part 1 flyers. It exists both as a one piece casting with the tab reading Megabot and a two piece casting using the same legs as the Roborgs.
There are two cockpits, two rear centre weapons and three drivers, plus one controller. The tab reads Roborg.