Looks like someone decided to convert it to percussion and then gave up - now that would have been something -
Someone did try to convert it, but it was to centerfire, not percussion. You see many original pinfires, that had angled firing pins fitted where you see the work done on yours. That would explain the missing hammers as well. They either tried to modify or replace the originals, and that is most likely why they are gone. Probably in some long gone gunsmith's junk box never to be seen again.