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The Sigma SA mount and lens electrical connector are ordered from Sigma. That part is easy.
The black aluminum spacer between the Contax N lens and the Sigma SA mount is custom CNC-machined.
The screw pattern of the Sigma SA mount and the Contax N lens has some conflict so the spacer would rotate the lens counterclockwise by a few degrees. As you can see in the 3rd picture the center line of the lens is pointing at letter 'S' of the Sigma logo not letter 'G'. Since the Makro-Sonnar 100/2.8 is completely circular with no rectangular baffles and also the hood is completely circular, this is not a problem.
The circuitry is based on a standard circuit board used for Contax N to Canon EF autofocus conversions, but enhanced with an additional circuitry tailored for use on Sigma SA. (Canon EF and Sigma SA are electrically similar but that does not mean they are electrically identical.)