Pentax K body + Nikon F lens
The flange focal depth should allow conversion, but...
Keep in mind that using a fullframe F lens will get you a crop factor of 1.6*, because of the APS-C sensor of the Pentax K body, you'll get a pretty high focal length multiplier (you'll get a smaller image frame). Find out more about focal length in this article if you're interested.
Don't forget that aperture control won't be available for every Nikon F version (there's a multitude of them, check out the different versions here).
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