I am not familiar with the lens but as you say it has a screw thread with a Pentax bayonet adapter this poses a couple of questions. Is it a 'pre-set' lens. That is one where you set the aperture then close the aperture ring down manually before you take the picture? Or the alternative is it will be an automatic stop down lens for screw threaded Pentax cameras.

Here there may be a problem. The Screw thread Pentax lens uses a plunger pin to close the apperture down whereas the Bayonet lens uses a sideways motion with a lever action within the camera to close the apperture. I don't think they are able to be converted. Is it possible to take a picture of the lens and another of the back of the lens so we can see what it is like.