I got a friendly machinist to re-do the 6-7/16" hole to 8.5" now.
It gives me a 1/4" border to attach an inner plate (which will contain the circularly placed holes) to. I think I can fit 7x 66 mm barely. 6 to be conservative.
I'm counting on this camera being heavy enough that the rotation of the Lazy Susan bearing won't induce vibration. Actually for f/stop, that's not a problem as it's done before exposure. It's the concept of an hand-powered leaf shutter that's gonna rock the boat, I guess.