I just bought a spitfire a couple of months ago on what I could only describe as a whim. Drove it home from leeds on the motorway and managed not
to prang it even though it was the first time I'd driven a classic.
I know it's a scary thought of getting back less but the best advice I can give is drive carefully (stating the obvious), give twice or three times
as much room to brake as a modern car and you should be ok.
My agreed value insurance came through in about a week so you shouldn't have long to wait. People don't wait long to take extra money off you