It would be tough to come up wit a more simple, foolproof design then one similar to the Baker hammerblock system. A true, English pattern intercepting sear design requires bunches of parts, very delicately fitted up, and, might be very difficult to engineer into the Lefever cocking hook, boxlock design-remember, the Lefever only looks like a sidelock, Tim. It is a boxlock.
The actual "need" for a mechanism to prevent accidental firing, on a limited production bird and clays use double, is likely slim to none. I'd like to believe the eventual users will be a thoughtful lot. Excepting a V grade Darne I once owned, none of my past guns has had them, and I've never had the need.
Best,
Ted
