Alcoa is supplying the aluminum sheet for the hoods on General Motors Corp.'s new '97 front-drive minivans, a deal that promises to be the largest contract for aluminum body sheet in GM's history. Alcoa is expected to furnish alloys 6111 and 2008 for at least five years. The hoods weigh 17 lbs. (7.7 kg), about 3 lbs. (1.4 kg) less than comparable plastic composites.