There's an older book I have that covers several Medium format camera systems, which has a section on the Pentax 67 camera that I've found to be useful - "How to Select and Use Medium Format Cameras" by Theodore DiSante. I got a copy when I got my Yashicamat 124G years ago, and found it to be helpful.
It's paperback and the binding broke, so I picked up a used copy off Amazon a couple years ago. It has a table showing the exposure compensation to use with the Pentax 67 and 135mm lens at various magnification ratios that may be of interest to you, and sections on metering and macro photography.
It's dated, but so are the cameras, and a lot of the material is relevant