Nice build- especially of the Airfix kit! You actually saw one of these being driven? There were only about a dozen made (and I understand that most have found their way to Japan). Granted replicas (based on Miuras or more common stock) are not quite as rare.
Definately if you're looking to build a Miura or Jota, check out the Hasegawa kits. They are lovely, every bit as good as a recent Tamiya kit- even have full engines. They're also easily availible.
Miura
Jota