I spoke with Eric Johnston from OConnor, and he clarified that the O-Box WM will work great with a fixed lens like the 24-70 with a few extra parts.
He suggested I add:
Bellows Ring for O-Box 150-114mm
Reduction Ring 114-110
Chrosziel Flexi-Insert Rigng 110:50/85
to use my fixed lenses.
I also went with the O-Focus DM Photo lens set.
and paired this with the Zacuto Rod Riser for Scarlet/Epic and the Zacuto C300 Studio Baseplate (which I purchased separately rather than in the package, as I got an extra set of rods) and the Wooden A-Box.
This should give me an adequate tripod based rig (very inexpensive and lightweight), to which I can add handles, rods on the sides for articulating arms, rods on the back of the Studio Baseplate for a cheeseplate, battery, shoulder pad, etc. - which should work for me as I don't intend to work shoulder mounted - but do want the option to add shoulder mount for very sparse usage.
Most of what I plan (plans change of course), will be on sliders and dollies and jibs and use motion control.
If I really need something hand held, I'd probably hire a Steadicam professional.
I purchased from AbelCine and have been very happy with their help.