I don't think the firing pins are off center,.
The pic of the face of the breech kind of makes it look as so at first glance. But I think it's more from the old imprint of the shell/case heads of the orig calibers,,one larger dia than the other.
From that it looks to me that it may have been a 'Cape Gun' or at least 2 different head size calibers.
The small Bead front sight and no signs of an old dove-taileded into place rifle type up front might suggest at least one bbl was a smoothbore.
The blank filled rear for a fold down single leaf for the rifle bbl.
All a guess of course. Nice looking 'gun'.
