After a lot of debate, I have decided not to fit the stereo in the instrument panel. Instead I am planning to fit a genuine Celica radio blank to the instrument panel and then put the stereo in the glovebox. The stereo is remote control, so it should work out well. I just couldn't cut a hole in a genuine GT panel like this.

The GT instrument panel (Japanese spec) has some slight differences compared to a standard LT/ST panel.

Here's what the GT panel looked like before I restored it.

I cleaned up the silver matting as good as possible and also restored the original chrome (silver) gauge surrounds. Note the 220km/hr Japanese spec speedo, cool stuff!

Also this panel came standard with a four way hazard switch. See the markings above the hazard switch for the 4 positions.

Here's the instrument panel now. Ready to go back into the car, only thing left is to fit the radio blank.

This is about the best pic I have to show what the silver material on the GT dash looks like.