Impressive sleuthing, Raimey. That is an interesting action design. With the trigger acting as the hammer sear, I would imagine the trigger pulls should be very crisp. But it looks like the mainspring is attached to the barrel lump, so how do you break the gun down?

It looks like there is a small projection coming through the trigger plate ahead of the trigger in the diagram - this would match a similar projection shown in the photo.

Such a long, long time to be gone, and a short time to be there.