The Britannia has done 17400 from the conversion and total is about 104000 miles but apparently a very well maintained car and looks very nice, certainly a nice specification.
The 412 is a spooky coincidence as I recently bought a bundle of Bristol Literature which turned up yesterday and amongst it is a photocopy of the original drivers handbook for this car.
There is a 401 coming up for auction as well with Charterhouse Auctioneers on the 7th August which looks like its worth checking out. The sale will be near Bridport.
https://www.charterhouse-auction.com/