We didn't do the whole process of converting from TD3 to Stunts. We took the models from a Blender file that was available in another forum from somebody who had done the conversion TD3 -> Blender and then, we had to make some touches to complete Blender -> Stunts. With the dashboard, we didn't have a way to read it from TD3, so I simply took screenshots and clipped them and then put them together. This means that this process, at least from our modest perspective, is non-reversible. But... if you do know the format in which these files are stored in TD3, then it should be possible.
If you were to do something like that, you would have to do some extra work. The car behaviour characteristics are likely entirely different from those of Stunts. We haven't imported that at all. So you would have to recreate that. And TD3 dashboard include a 3D-shape part too, with windshield cleaners and all that Stunts does not. They even have a ceiling mirror!
