Hi Peter and welcome to the club.
What a fascinating find. I wonder if Tony and Gordon ever had a scrap in the back. Sorry I can't help with details but hopefully you'll keep us updated with your progress. If you know the original number you might see it in old footage of Downing St. I guess there'll be armour plate etc all over it, if you get in a bump with a Fiat 500 I wonder who'll come off best.
Cheers
Pete