Sorry for the confusion. I do mean a Contax lens on an M body.
I know about the Amedeo adapters and they are indeed fine adapters but I would like the challenge of building an adapter myself.
I will use the adapter for internally mounted Contax RF lenses on my Leica SL with a close focus M-adapter L so I don’t need to worry about the accuracy a rangefinder adapter would require. I use my Contax lenses on a Contax rangefinder so my homemade adapter will never be used on an M rangefinder.