Fantastic work Hiro!
I really like the balsa and vacu-form technique ...true that the Mattel vac-u-form machine doesn't allow for very big pieces to be made
For the dash grills, it might be possible to use wire adhered from beneath styrene panel, but if wanted flush then using fine wire bent in center to raise up, or alternately, mildly scratch backside of panel (with scriber) slightly to recess wire closer to top surface