Here's a hack method - note how it effects the rotating C3 sprite though! I also have not tried with varying the camera, but I imagine it should be ok.
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Thanks so much for that :) . Looking at it it seems everything by default for some reason is backfacing (you can see the text rendered, even if on a '2D' layer, disappears with back culling).
It'll be a bit awkward, and limiting/additional steps+triangles required (duplicated and normals flipped) to fix areas of a model you actually need to see both sides of. However for the scope of the game I'm wanting to make, this solution will allow me the end result I'm looking for so thank you very much for that. The trick required to finish the effect is having to flip all 3DObject normals before exporting, that way you can hide the 'front facing' faces (that are now back facing), and hide front-facing instead. This way regular construct objects (at least besides construct 3d shapes) will stay visible.