AT THE MOVIES, Porky’s, another 1950s coming-of-age flick, swaps Diner’s nuances for nudity — and goes on to become the fourth biggest film of the year. After two sequels, its cast of unknown actors (right) are still unknown. IN BOOKSTORES, North and South, John Jakes’ sweeping novel about the Civil War, is the No. 2 fiction best-seller. Three years later, the book will become a $25 million ABC miniseries starring Patrick Swayze. THE SOUNDTRACK to Chariots of Fire reaches No. 8 on Billboard’s Hot 100 chart and is on its way to becoming the best-selling instrumental film score of all time — until Titanic barges in 15 years later. AND IN THE NEWS, Argentinean troops storm and conquer the Falkland Islands, a British-held territory off the coast of Argentina. The invasion ignites a war between the two countries that ends when Argentina surrenders on June 14.