I was at Lakes at Wyboston this afternoon, and they have a very pretty (albeit very minor accident damaged front bumper and headlamp) 1989 340 DL for sale. They say they want £600 for it. It doesn't appear to have tax, and presumably no MOT. I had a quick look at the usual rot points (arches, rear sills) and all seems solid. Odometer says 94,000 miles. It's not mint by far, but pretty tidy, and has a nice original look to it. It interestingly has a 5-speed gearbox in DL spec.
I thought I'd just put it up in case anyone is interested - it looks like it's well worth saving.