Thank you very much for your answers!
Of course I will first fit it to the car and then let it be painted.
The picture from under the car is very helpfull to me as it shows, how the valance is fitted to the car. That is what I need to know. I think, it does not show a Morgan made valance, but I hope, it works the same way. More pics from under the car would be great, if there are any around.
Thank you very much again and I will post the result, if I will understand one day, how to put pics on this site! ;-)