If you have ever looked at a CR2 file, you can spot differences between figure (uses a figureResFile to load the whole figure OBJ and geomHandlerGeom to assign the groups to actors) and prop geometry (uses an objFileGeom to load a single actor's OBJ). But, you can actually make a rigged figure from individual prop geometry alone. For mechanical parts like a car, which don't bend when the actors rotate, this is easier to do. If every body part of the car figure references a separate OBJ file, you'll get what you expect.

This is the way that Poser handles replacing a body part with a prop.

I will admit that I am yet to claim any mastery of the setup room, because I've spent 20+ years hand editing CR2 files, since the setup room has yet to gain my trust, and did not exist when I began ;-). Learning Setup is on my "To procrastinate about forever" list ;-) [No! Bad hand!]

I concur 100% with Morkonan's assessment of ensuring that the internal bone names exactly match the group names you want for your body part actors.

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