LATER this week a huge piece of history is expected to be suspended over downtown San FranciscoA 15ton section of the Titanics hull the largest piece of the sunken luxury liner ever recovered will be lifted four stories by crane and installed at the Metreon as part of the show Titanic The Artifact Exhibition opening June 10The hull most recently on view in Las Vegas is sitting in a Southern California warehouse waiting to be delivered to San Francisco by flatbed truck Its part of an exhibit of hundreds of items recovered from the ship which sank April 15 1912 killing 1522 of its 2227 passengers