I got a Contax / Yashika fit Carl Zeiss S Planar 60mm f/2.8 macro a couple of weeks a go through the usuall online auction site. I had intended to get one of the Leitax conversion mounts but as I was too impatient to order one and I have a lathe I had a go at making a mount.
I got an old K mount off a badly damaged tokina and soldered / machined it to the dimensions of the original mount. This gives me focus from infinity to 1:1. Here is one of the first test shots (1/30, approx F/16, ISO 100):
I have since started converting it from M to A. I have added electrical contacts and made / fitted a new aperture lever. It can be used in all exposure modes now but needs progressively more negative exposure compensation as the lens is stopped down. Need to devise a mechanism to convert the linear diameter change of the aperture to a linear area change. In spite of this it still workes qite well.