I have a section of GM 40x13/16 that can be reamed to about a .410-.420. The Chambers Ketland is a fine rfle lock but too big for a pistol. I have made some good pistol locks for the German market,nice looking,fast and about the same configuration as the L&R small Manton. I no longer make them but can use the external parts for the L&R,fitted internally with a benchcrafted mechanism.
If you are interested,contact me at<wvgzr@webtv.net>
I have no idea about a single set trigger. They are a labor intensive device and I haven't made on for 30 years.
Bob Roller