Mighty Mercs including the 6.3 and 6.9. Amazingly the 6.3 was roughly 5 times the price of an XYGTHO when new!! If that ratio remained the same through the decades, a 6.3 would be worth around $2.5M today!!
http://www.uniquecarsmag.com.au/news-and-reviews/article/articleid/86138.aspx
http://www.uniquecarsmag.com.au/news-and-reviews/article/articleid/86138.aspx