Here are some photos of the action with the stock off of it. I was mistaken in saying that the gun was a sideplated boxlock. It is in fact a sidelock, but it is a reversed sidelock, I guess you would call it. The plates that the lockwork mounts to are internal and removable from the frame. And the outside covers are just that, covers. I have seen similar to this before. But not this specific action design.
The sears are part of the hammers and engage with a solid block attached to the internal plate. The last photo shows the gun cocked.
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