LOUISVILLE, Ky. – Few Kentucky Derby stories have been more compelling in recent years than the one involving General Quarters, but the sequels haven’t been bad, either. Owned and trained by retired high school principal Tom McCarthy, the 5-year-old horse stands a chance to tack on another remarkable tale Sunday when going postward as the 119-pound highweight in the Grade 2, $175,000 Firecracker Handicap, the closing-day feature of the 39-day spring meet at Churchill Downs.