I seem to remember that Huets had a white Mk2 as a demo car several years ago, and they actually had an Alpine 6 disc changer tucked behind those vents - they modded them so that they would fold down so that the magazine could be ejected etc.
I personally think it
would be possible, as most things tend to be if you throw enough time/money at them! As Veedub says, you will need to modify your heating/ventialtion system otherwise you'll be chuffing hot air all over your headunit, which if it has thermal protection will sht it down.
I would suggest going to find a car as complete as possible in a scrap yard - you can have a play without butchering your own car then
