Franz Schafhausen of Hildesheim learned his master craft from a French Arquebusier and apparently received his gunmaking sheepskin as a French apprentice. His stint was from the mid to late 1800 and then his son Friedrich took the reins and pressed on till say 1972 when Wolfgang Paulus was the owner.
I have seen ejector BBFs and Drillings but they are few & far between.
The two bases are for either 2 different bullets or 2 different sighting distances in different environments; like close & far.... Long distance Corn Field shot vs Mt terrain. A hunter would have been well equipped to have such a choice.
On the Gunsmith, I would check with the likes of NECG(New England Custom Gun), Larry Schuknecht of German Hunting Guns or maybe even JJ Perodeau.