I don't want to hijack this thread, but my issue is close to being on topic in a way. I have a Mamiya 7 rangefinder, a 6x7 format, and a Hasselblad for more flexibility (close focusing particularly). The RZ/RB's are just too dam big.

I LOVE the 6x7 ratio and want to mark the Hass focusing screen for that ratio to crop at the time of composition. Any suggestions on exactly how to do that? I've had a hard time finding methods that seemed practical. Seems like there should be an easy solution, but have not found it. Any suggestions from you experts?