As long as it's animated spaghetti you're actually pretty close. Basically just toggle every export setting on fbx animations until it works. (scaling method, axes) There really isn't a "do this, it works" - make sure your bone names match the Kunos ones if you can, and the rest is up to you to find out something that works.
Also you are making it about 100x harder if you want it to work on existing animations. It is much better to export driver + driver animations at the same time, on the same export settings, for the same car+seating position.