The Morphy description stated the bore diameter of the lower barrel is .398", at the muzzle(choke). This is too small (in my opinion) for the original caliber to have been one of the Lancasters. This brings us back to the 9.3X74R, as Raimey opined in the beginning. Even if the barrel wasn't very good, it seems like a poor conversion, in spite of my opinion that the previous owner could do whatever he wanted with it.
Mike