In the chassis designing and modding stage of the car production, it would be really helpful to have some sort of measurement tool. By this I mean that each individual part so a headlight for example should have a Width x Depth x Height (or if its circular a circumference and diameter) measurement as well as maybe having an area measurement. Also it would be good to have measurements of how far away the centre of the object is away from all of the sides, this way it would be a hell of a lot easier to line up handles precisely, rather than doing it just by eye, and the same could apply with having numerous headlights and tail-lights on a car body. To add to this you maybe could be able to edit one of the values by hand, so by this I mean having some sort of text box whereby you can literally change the values by simply typing them in, which in my mind would be a lot more efficient in terms of genuine car design. My idea for the aesthetics of this would be simple, when you are moving around the object the values would be opaque so not distracting but still readable, and when the object stops moving the values become solid and editable.
I hope you found this suggestion helpful, and if this has come up before, I hope it further reinforces the idea of measurement, anyway have fun replying away! 