Hi Daniel,
you don’t really need to select a machine in Fusion360 to be able to generate G-code for it. Fusion360 recently introduced new Machine Simulation capabilities, which we discussed in that thread and @neilferreri even had a prototype running for Shapeoko 3D simulation, which was nice but ultimately…not immensely useful.
To the best of my knowledge, the post-processing part is unchanged so you should still be able to use a suitable post-processor for the Shapeoko (C3D’s or Neil’s), and just ignore the “machine list” (or select a generic machine to keep Fusion360 menus happy, but they won’t be used unless you tell it too, in the simulation mode)