G-Scale Train Engine 3D Model

I have a G-scale locomotive project underway and I need a clean, well-structured 3D model of the engine so it drops straight into the larger assembly I’m building. The job is strictly 3D modelling—no drawings or simulations—yet I still need each visible component called out in reasonable detail: boiler, cab, trucks, wheels, valve gear, couplers, handrails, and any external piping. Internal parts that never see daylight can stay simplified; everything else should be dimensionally accurate to real G-scale so mating features line up when I place the file inside the complete train set.

Preferred workflow is any mainstream solid modeller (Fusion 360, SolidWorks, Inventor, or similar). At hand-off I’ll need:
• Native file
• STEP file for cross-platform use
• A lightweight format such as FBX or OBJ for fast previews

I’ll run a fit-check inside my master assembly; if the model inserts with no scale drift and all major parts are separately selectable, we’re good.