Tapped the bottom plate with 4-40 threads for four socket cap screws and two phillips heads.
Above is everything fastened together to test the fit.
Starting to refine the forms of the brass parts, above is a side view of the telegraph key itself, marked to remove metal.
Top view of the telegraph key.
Above are two images of the finished telegraph key, along with the tools I used for removing and shaping the metal. The hole in the center of the key has been drilled and tapped for a 4-40 socket cap screw as well.