I recently found this old 6x7 brochure when going through my files. I think I originally found it in a junk shop, and it seems to date from the earliest days of the 6x7. There is no reference to a mirror up function, and one page has a picture showing it alongside the other Pentax cameras, which are Spotmatics.
The brochure shows a full range of lenses and accessories though, including those in the second picture. That 800mm f4 is a monster (nearly 18kg they say) and I wonder how many were made. I have the 300mm f4, second from the left in the back row, and that seems huge to me, but it is dwarfed by that 800mm.