I don’t have a Fuj GX680 but I do have a Mamiya RZ67, sometimes coupled with a tilt+shift adaptor, which gets close to the weight and bulk of the GX680.
I am now happy with an Arca Swiss type plate and clamp but it took some time to come up with the solution, and it wasn’t cheap.
I have two Manfrotto tripods which use the hexagonal plates. However, when the hex plates are screwed directly to the camera, the camera can accidentally swivel about 5 degrees horizontally, which is enough to affect the composition, radically so with a close-up image. The knurled knob doesn’t make it easy to attach the plate really tightly.
However the RZ, along with Mamiya RB and 645 systems, has two small threaded holes, either side of the central hole, to accommodate anti-twist screws. Presumably Mamiya made a custom tripod plate at some point but I’ve never seen one.
For a while I toyed with the idea of drilling through the hex plate and fitting anti-twist screws, but my complete lack of DIY skills made that difficult. Eventually I purchased an Arca Swiss plate custom-designed for the Mamiya:
https://www.robertwhite.co.uk/arca-swiss-quick-release-mamiya-rb-rz-50mm-camera-plate-1-4.html However the plate by itself isn’t much use without a clamp to attach it to. Now I had a choice of abandoning the existing tripod heads and purchasing an Arca Swiss-compatible head, or buying a clamp which was capable of attaching to the hex-shaped space on my Manfrotto heads.
I found this -
http://www.wexphotographic.com/buy-kirk-sqrc-hex-manfrotto-hex-plate-quick-release-clamp/p1557169 which fits onto the Manfrotto heads. Again it’s not cheap but I share it between two heads and two new heads would have been much more expensive.
So now I have a rock-solid system for supporting the RZ without unwanted movement. My camera bag is heavier and my wallet is lighter.
If you’re not familiar with the Arca Swiss system there is a good description here -
https://photographylife.com/arca-swiss-quick-release-system