Bob Michaels
nobody special
..... I love the mamiya 6 as a camera, but not sold on the 6x6 format. I find it restrictive.
Why not just crop your 6x6 images to 5.14x6 which gives you the 6x7 aspect ratio or whatever you want. That saves buying a new camera and lenses. I once shot a lot of 6x6 but most often cropped to 8x10 aspect ratio. In fact, almost none of my Mamiya 7 photos end up as 6x7 aspect ratio but cropped / trimmed ever so slightly to 8x10 ratio to reuse existing mats.
Don't let arithmetic rule your artistic vision.