Based on the actual exposed image area in the scans, horizontal I got about 9063x7000 => 5:4 which matches the 56x70 nominal 6x7 frame. Nowhere close to 6x7.5 that I've seen claimed. Most likely my ProS body is just about old enough not to have the 6x8 baffles, or maybe my revolving back adapter isn't the right one. I could see more mask area on the negative (a little light scatter), but there was no image in it.
Mind you, this was done with the 50 mm lens, which is said to not cover the 6x8 frame. Depending exactly how the retrofocal optics work (50 mm focal length on a 112 mm flange distance), a 65 might get "under" the baffles better and expose a wider negative (which should also be true with other lenses; I'll probably try a roll in the 23 back with my 90 mm for comparison, or at least mount the 23 shell and look for lens access from the frame corners).