A body found in the back seat of a sports car has been identified as that of David Tong, one-time member of a Chinese gang and the brother of a San Francisco policeman. Tong's badly decomposed body was discovered by a meter maid patrolling in San Francisco's Sunset District when she spotted the car with three tickets on the windshield. A coroner's spokesman said Tong had been dead at least a week. Police said it appeared Tong had been shot once in the head. Tong's brother, Officer Richard Tong, had reported him missing. David Tong, then 21, Kevin Gee, 22, and Gary Pon, 23, were convicted in the November, 1982, kidnaping of a 24-year-old woman after Tong's police officer brother testified about a series of telephone calls he received from his younger brother the day of the kidnaping. Tong was sentenced to three years in prison. Pon and Gee received one-year terms.