Maybe I was wrong about ours being the same. It's difficult to see with your picture. This is from W.W. Greener's book The Gun and it's Development page 141. Does that look like yours? The flat spring has a hole in the wide end that the screw on frame in front of the lever goes through and a 90 degree bend in the tip of the short end. Mine wasn't dove tailed in. It was a tight fit, but with a bit of work it came right out. There are a couple of poor photos of the action on my short 10.
edit: Just took a closer look at your picture, Hugh.They're not the same design. Mine is like the one in the Greener book with just the single Purdey bite. It was made in 1872.
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Threaded Mode