The DOF marks on the Mamiya Press lenses are at least one stop optimistic compared to most modern DOF marks. IIRC, I computed that they correspond to a circle of confusion of 0.1mm, while 0.07mm would be more standard for 6x9 format, and even then for "critical" work one would want to go at least another stop more conservative.
Wide angle aux viewfinders generally have some distortion (typically barrel) by their nature/optical design, if you also need critical leveling it may be useful to put a bubble level on the camera top.
Wide angle aux viewfinders generally have some distortion (typically barrel) by their nature/optical design, if you also need critical leveling it may be useful to put a bubble level on the camera top.