Can't see the dummy filler cap on the left, I've tried saving the pic then zooming in, still can't see one so I'd say it is a GT. GT was introduced in Europe in 1995 and UK in 1996 so the year is about right (although if I am being blind and there is a dummy filler cap on the left it is possible that it could be an earlier car but registered in 1996 so I'm open to correction!).
You're right Grigio Vulcano is a lovely colour, only seen one other UK GT in this colour and one Cup.
Aerial position is interesting as you say. I've only seen a few with the aerial mounted there and all of those have had an electric retractable one rather than the fixed one this car has. I've also seen one car that had both a the normal type roof aerial and one mounted on the rear wing, maybe it had two radios!