Hi Andy and Carl,
I made the lock from castings by Blackley's. The castings included the frizzen, plate, flintcock, top jaw, sear, bridle, tumbler, safety slide, and safety bolt. I made all lock springs, screws, fly, stirrup, and safety spring. I eventually made my own bridles as well. The lock is one of a pair I built.
The safety thumb slide has a horizontal bar that fits through a slot in the lock plate. That bar is morticed and pinned within the sliding bolt that locks the tumbler. You can see the end of the bar in its mortice in several of the photos. The end of the bolt has a little raised nub on it. That nub rubs against the little raised nub you can see on the inside of the "wing-shaped" safety spring. When the safety is slid back, the nub on the spring pushes the nub on the bolt back holding it in the off position. When slid forward, the nub on the bolt slides over the nub on the spring and the spring holds the slide in the forward "on" position. The small pistol locks were hard to make because all of the screw holes, slots, and mortices were tiny and had to be very precise.
dave