You're just about dead on for what I paid, Rocketman, except I paid AUD.
In the close-up of the side of the breech, there is a definite seam in the metal; there is a yellowish discolouration on the top of the breech which looks like old brazing; the hammers are lovely, and match, but are too small for the engraving on the locks. It all points to a pinfire conversion, but possibly of a rifle - the back of the trigger guard is quite stout, the stock is thick and strong, the steel-capped pistol hand looks very rifle-like to me. The serial number appears no fewer than 6 times - but nowhere on the barrels or forend.
Perhaps this was built on pinfire in the late 1860s, and was obsolete before it even left the maker; maybe it was converted (perhaps before it was even sold?) with a set of barrels off another gun in the workshop - hence the two different addresses - the stamped address on the flats a later one when that work was done?
But then, how early did rebounding locks appear? Maybe that was tweaked later...
At any rate, it'll be a fun shooter with short-chambered BP handloads...
