Welcome to the board! Pinfire guns and cartridges are a rarity nowadays, and there sure can't be too many competent people on the board!
Interesting pistol. Wasn't this setup with protruding nipples the original Lefaucheaux's idea, the pinfire cartridge being a later development?
In Russia, steel shells for centerfire guns which used the same idea of shooting muzzleloading primers were available till the end of XIX century. Naturally, the nipple was placed in an indentation on the bottom of the shell; the recommended procedure was to load the gun from the muzzle and then replace the primer by breaking the gun open. Slow and awkward, but probably saved someone's trip in the depths of Siberia. I haven't ever seen one, though, only read about them.
Re: sidelock vs boxlock, we don't usually distinguish between them when talking about hammer guns. Although if the line had to be drawn, this pistol would surely be a sidelock, with the lock parts fitted to a plate on the side of the gun. Your shotgun, on the other hand, ought to be called a boxlock, despite having a side hammer, since its lock parts apparently are fitted inside a box-shaped action. However, as I said already, the "sidelock-boxlock" opposition is normally reserved for hammerless guns, a hammer gun is just a hammer gun.
