A bit of history. Ashahi
purchased the name Pentax from Zeiss. Also the original Pentax K 28/2 is a design copy of the Zeiss "Hollywood" lens, that Pentax received from Zeiss in a trade (rumored). There is also
cooperation on the Pentax SMC and Zeiss T* coatings. Zeiss also helped with the K mount design - thus the C/Y mount incompatibilities. For what ever reason the two companies went their separate ways and Zeiss partnered with Yashica to build the Contax line of cameras and lenses. The C/Y mount is nearly a copy of the K mount with two important differences. 1) a very small difference in the registration distance, and 2) the thickness of the flanges on the mount. So, the lenses are not perfectly interchangeable, and no adapter is possible due to essentially the same registration distance.
So, no the adapter really will not work as I believe you intend it to, because it will set the lens too far away from the sensor (the registration distance). If these were Contax lenses, I would recommend the Leitax.com mount kit - remove the C/Y mount and replace it with a K mount. The parts run $100 per lens. This approach might not be cost effect for these lenses. Also, the Leitax mount kit is made for the tollarances of the Contax lens. The DSB mounts may vary in thickness from the Contax mounts.
What you could do is to shave the C/Y mounts. You would not want to do this to the Contax lens, since it would depreciate their value instantly. It probably does not matter so much for the DSB. So here is a post from RioRico - a legend here (who no longer posts due to his eyesight). But first - back to some history. The Pentax K and C/Y mounts are essentially the same - really both designed by Zeiss. However the C/Y adds a kicker by making the flanges a bit thicker so that the lenses would not be interchangeable. That is why you can't twist them on. Here is a shaving Rico's technique (I would suggest reading the entire thread).....
I would also suggest buying a very cheap set of K mount extension tubes at about $10 or so. In this way you can mount the lens on the extension tubes and essentially see or view from the inside of the camera, as to what is going on the interior of the mount - another trick from Rico.
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from evil bay - the 135 goes for about $40 to $80 and the 28 goes for about $90 to $125.
Actually, the Yashicas are pretty decent lenses. Zeiss in teaching them to build the Contax line, transferred the knowledge to their Yachica line. The DSB's are the consumer line, with the ML being the premium line.