Wrecked the Valiant. Pictures here.

You need to be fighting this money figure they came up with. Classic cars can be "argued" into a different category than some "blue book" market value. One way is to challenge them to come up with a replacement car in comparable shape for that amount. You and I both know it cannot be done

If it was not already insured as a classic, it's worth whatever they say. You cannot "change" coverage after an accident that I know of.