My 91 Trans Am just seems to have a massive hole where the stereo belongs -
I have no idea what the original system in there was. I have plastic fascia
covers to cut the hole down to the right size, but can't work out how to
secure the head unit in there (standard size Kenwood). There's nothing to
stick the mounting cage onto because the hole is about twice the size of it.
Any ideas?

Cheers,
Dan