Pentax has produced a 300mm EDIF lens that I have tried, but didn't purchase because I couldn't afford it at the time, that is really outstanding, the older 300mm lens is also very, very good. They have also produced a modern 400mm 4.0 and an 800 6.7 lens. These last 2 lenses are very large and very heavy and very expensive, although possibly could be purchased used for a reasonable price. I believe that the 300 EFIF and 400mm EDIF 4.0 are reviewed on photo.net. The older lenses, like the 600mm 4.0 are preset lenses.

I have an older 67 that has mlu and I replaced the screen with a Maxwell screen, which is great. If you are contemplating using the longer lenses, be sure to use a really solid tripod, tripod head, and camera to head mount (mine is a Kirk, I think, or Really Right Stuff, can't remember). Camera to tripod head mounts that don't have a metal pin that goes into the body and are not well made allow for too much movement with the big 67 shutter. I get superb results from my 67 now that I have the Maxwell screen and a solid camera to tripod head mount with the 45mm, 75mm, 135mm, and 165mm lenses, all of which I recommend highly. I occasionally use the 2x converter on the 135 and 165, but I have noticed that I need to hang additional weight on the tripod to get the sharpness I want with the higher magnification. I absolutely love the Pentax 67 body and lenses and also use it handheld with the 165 2.8 lens for portraits often with no problems.

You shouldn't have problems with the screen on a new 67II, it is a modern, bright screen. Good luck.
Doug Webb