Your main thing that will cause concern is that it will have to be able to be seen by toll cameras and of course the
"safety cameras" errrr "safety". err well you know the ones I mean.
I recently read a thread on one of the US forums where a P owner was having handling problems at speed with his car, after checking everything that could be checked, suspension, steering, tyres etc etc,....it came down to the re positioning of where he had placed his number plate. He had actually placed it slightly to one side but it had caused the handling problems. Put the plate back to where it was supposed to be and handling problems ceased.
Just food for thought. That was a street car not a track car....