That's not really much help as the Bullet terminology is specific to Bullet, the Godot implementation is specific to the original Godot physics API(Even though 3.0 is Bullet underneath). I'm not getting anything to work following the 2.0 docs though, so I suspect there are subtle differences in the 3.0 implementation.
TBH I was just looking for some a simple vehicle project that works with 3.0 Beta 1 if possible. I don't need anything sophisticated just 4 wheels and body, which is steerable.