An American icon, the double-planked mahogany and brushed stainless steel Thunderbird just returned to the annual Concours d’Elegance on Lake Tahoe, California, after some refurbishing. Built in 1940, the 55-foot-long Thunderbird is powered by two V-12 Allison P-38 Lightening aircraft engines that produce a top speed of 70 mph. Thunderbird was built for George Whittell, Jr., a wealthy and reclusive playboy who also owned a Grumman Goose seaplane and six Duesenbergs. He built a 100-foot long boathouse for the boat and a 600-foot tunnel to connect it to his main house on Tahoe’s west shore. Designed by John L. Hacker, of…