mamaflinter, so far I'm getting similar results. I need to find Stephen Alexander in, I believe, Geneseo, IL. I saw a photograph of a lock he made in a Muzzle Blasts from 2000.
Something that has been percolating is: Does a standard lock plate -- an L & R "Durs Egg" or "Late Manton", for instance -- have sufficient mass behind the cock to allow fitting of a mirror-imaged Mortimer safety assembly? The procedure would also require milling a slot in the tumbler. Dunno. I have neither drawings of Mortimer S.438, or either L & R flintlock, so I have no way of verifying either way.