According to http://www.dexigner.com/product/news-g12107.html Dean owned one of these 1967 Ferrari 412P on exhibit at the Cincinnati Art Museum. This is collborated by a commercial on the HDtht channel, which gives the following info: raced by the Belgium team Ecurie Francorchamps, owned by Harry Yeaggy, and was featured in the Cincinnati Art Museum from Nov 2007 to Jan 2008 http://www.designtaxi.com/news.php?id=13507
Also, just found a collaboration http://www.austin360.com/blogs/content/oh/story/entertainment/events/2007/12/26/fe122707calendar.html
Exhibit of the 1967 412P Ferrari. On loan from Harry Yeaggy, car has been owned by Hollywood movie mogul, John Calley and actor James Coburn, as well as Dean Martin Jr. and Cincinnati's own Carl Lindner. Through Jan. 6. Cincinnati Art Museum.
the Facel Vega I posted about last year http://justacarguy.blogspot.com/2009/03/dean-martin-and-facel-vega.html
from what I could learn in searching the internet, Dean owned this Ghis L 6.4, a 1967 De Tomaso Mangusta Fantuzzi Targa, a 1966 Ferrari 330 GTC, and a 1972 Cadillac station wagon: http://justacarguy.blogspot.com/2009/03/1972-cadillac-station-wagon-1-of-2-made.html
If you loved Dean Martin, and want to check out a really cool laid back blog about him, his movies, some stills, and some video clips, ya gotta go see http://ilovedinomartin.blogspot.com/