Here is an example file for the 3D Viewer scenes used in projects like Flufs Unleashed, PB Swappables, Raicers, Karts, TNL, Goblins, and many others.
scene

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Dimensions 3D Viewer Scene

Build assets at a 1:1 ratio, using a base human height of 1.8 meters as a guideline for most human models. Some scenes may require asset-specific adjustments.
image(32)

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Textures Atlas 3D Viewer Scenes

Assets should be packed into a single master material ideally or max 3 materials for each scene in total as an example below:
image(33)

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Color Swatches 3D Viewer Scenes

Use Color swatches for assets that are solid color (embedded within Master Texture atlas)
image(34)

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Sample Scene 3D Viewer

Here is a sample Blender scene it contains the scene presented above: SM_FU_GarageScene_LOD0_Example.blend