Cannot give you pictures as it would require complete disassembly of the butt plate and patchbox; however, I will try to explain how mine is built.
The lever that catches the rivet in the lid of the patchbox is one piece and is quite similar to a gate latch. Push down on one end (protrusion behind cheek piece) and the catch end securing the patchbox rivet lifts up, releasing the patchbox door. A flat spring is located in the wood on the patchbox end of the lever to hold the lever. Careful layout is required to make this one. The lever was made long and fitted into the butt under the plate and filed to final shape, removing it and reinstalling many, many times. No wonder it was used very little.