I'm not aware of a PB -> M42 adapter. The mount would be too big to fit inside the 42mm mount (I think?). Well...the lenses would not reach infinity since the register distance is 44.4mm and Pentax is 45.46mm.
As usual...you "may" be able to convert the mount itself to PK. But, you might as well line up with the rest of us looking for M42 Zeiss lenses.
Sorry...I wish it could happen too
