This was in Bell of Africa.

He went to the Yukon with a single shot in .360 by Fraser, not a Mauser. It was a Farquharsen falling block. He took 160 cartridges.

He didn't work for Fraser, at least he doesn't say so, but he said they were good friends. The Mannlicher Shcoenauer from Fraser may or may not have been customised; he doesnt say anything about it that doesnt fit a factory MS carbine as far as I can tell, and the phrase 'whittling away at it till it was five pounds' is an interpretation of the magazine article writer, there is no reference to anything like that in Bell's books or articles. (The photo of the rifle that is suppossed to be the same one in American Rifleman certainly looks like a standard ms carbine, although it has a cocking piece aperture sight - this may be a later addition, Bell wrote he never used anything but open V sights in Africa, although he did use them in later life.)