I have attempted this!!! I have removed the dials and removed the motors that move the needles, very carefully removing the needles these can snap very easily. Removed the blue dial and unscrewed 2 screws. I found a company on the net that sales plastics I have order a blue sheet but it arrived and I think it is to dark, so I will order some more. The hard part is cutting the blue plastic to size and drilling the holes for the needles and screws. I have got my self a spare dial box, which I will test on first.
Will post again to let you all now how I get on, if any one would like to find out more, reply to the post of email me at mailto:g.palfreman@virgin.net">g.palfreman@virgin.net