As others have stated, no Mk III carbine was ever produced at the factory, although some were issued...probably....but not to the military. The M10 .280 Military Match did not have the committee designed magazine found on the Mk III--it had an enclosed box magazine in the stock, similar to the M1907 Deer Stalker sporter. The RNWMP carbine is of course a 1903 so totally different. I have both and can post photos. There were Mk III rifles cut down for use by possibly the Rangers or guards, but they look like a slightly better done Bubba rifle, with 24" barrel, no front band, stock cut back to in front of the rear band. Usually no stock marks but do have a nice crown job (as opposed to the usual straight(ish) Bubba bob) and a standard front sight with hood, standard rearsight, not drilled for scope, etc. Kind of a handy-ish sporterized Mk III. I've owned more than one over the years. Without photos, I would say that is likely what you have. So, didn't leave the factory that way, but was sort of issued, although some dispute that and think they were just pretty professional cut down jobs done by the Trade in Britain after the Rosses were released for public sale.
Ed