Thanks for the point. I didn't word my post very well - it's not so much the prototype, rather the buck for the prototype which would provide the moulds for the production car.
This is the Neretti I and I think the Neretti II came out in 1971. Oddly enough, the latter car is not nearly so attractive, but has lines which reflect the styling of the time. It's probably the later car which was the subject of the earlier puzzle.