SOUTHFIELD, MI—Gail and Milt Greenblatt, parents of soap-opera star Brett Green, are beaming with pride that their son is a doctor on ABC's All My Children. "Dr. Cord Montgomery graduated from Harvard Medical School at the top of his class," Gail told a neighbor Monday. "What's more, he's the youngest surgeon at Pine Valley's top hospital." Milt expressed relief that his son has left behind the "rough crowd" he ran with last fall as a bully on Gilmore Girls.