I've not made any progress in the matter of dates, but have found images of guns with some similar features, albeit not an exact or complete set in either case.
[img]
https://www.dropbox.com/s/g4p77km6iik2g9u/Adolf-Frank-hammer-drilling-RH.jpg?dl=0[/img]
A drilling by Adolf Frank based on an 1894 patent chambered for 16 Ga/8mm JR (Guns International). This has similar action profiling and decoration to the gun under discussion here. Unfortunately the seller's description doesn't show the proof marks or give a date.
[img]
https://www.dropbox.com/s/3nibjllr61j686u/Stiegele-combi-Lefaucheux.jpg?dl=0[/img]
A combination gun by Carl Stiegele chambered in 16 Ga/9.9x47R; "Manufactured circa 1894" (Simpson Ltd). An earlier and more flamboyant gun than the one under discussion here, but the only other I have yet seen with this type of Lefaucheux action.
