The frames are only 76mm long so unless the spacing is whack, it should just fit. I figure the spacing has to be reasonably tight or the 9 frames won't fit on a roll of 120; at 10mm spacing there is no head/tail left to grip during developing!

I'd be interested to hear how you go with the GX680. I too have an RZ and use it 95% of the time, I like the idea of 6x8 but can't see myself lugging the GX680 everywhere or handholding it.