Thanks Clive, Richardo, John, Mike and Greg for your appreciation!
Yes, the 300EDIF for 67 series is the lens to go
Mike, the Proline 16803 is an outstanding camera, it never let me down once and, as you are seeing with yours, the raw frames are extremely clean!
Greg, I made my adapter in a friend's shop back in Italy. I started from a Pentax 67 extension tube. Attached are some pics of the adapter and the adapter mounted on a custom made dovetail I designed. On one side you can also see the robofocus and belt system.
Let me know if this can help. About Pentax lenses, so far the only one I have used is the 300mm EDIF, using my telescope remotely I have no possibility to change lenses as I want..
Clear Skies!
Marco