Dr FM, you might be interested in getting yourself a copy of Graeme Wright's "Shooting the British Double Rifle". The man in the photos above, Vic Pedersen, is credited in that book for his gunsmithing skill (he is retired, pretty-much, these days). The first photo, in black-and-white, is in that book. Vic lives in Darwin, and you could try calling him on the telephone (he may or may not wish to talk).