The second design came about as an idea to get away from tracking down 3/8 square stock and some way to bend it, while it still uses 3/8 square stock in this model, it gets away from the large zig-zag bend most designs have, allowing for and unbent primary lever, and a secondary lever under much less strain to the point it could be made from wood even. These are connected by a simple sliding pin. I speculate canting this pin backwards may be helpful, giving you a longer, but lighter trigger pull. A single compression spring could be used for both levers by simply drilling through the wood between them ahead of the privet for the primary lever and behind that of the secondary lever, and would be held captive by the secondary lever once attached. Like a pinlock design, some means would be needed to keep the lever from rotating too far away from the stock. A similar modification could be made to a claplock design as well. Also credit to the plans on alcheminc.com, which inspired the design.
The model is publicly available here.