I should have wrote: Sometimes with 6x8 back you will also get dark, round corners. This is due to filter vignetting. not 6x9 back
Andre Noble, Beverly Hills California http://andrenoble.com/
I feel better now that I've seen the notation in Mamiya literature you've pointed out. Kind of a poor implementation I think. I just ordered a 6x7 back.
Develop, stop, fix.... wait.... where's my film?