Mix flour, pineapple, 1 1/2 cups white sugar, oil, egg whites, baking soda, and salt together in a bowl; pour into a 9x13-inch baking dish.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 35 to 40 minutes.
Heat 2/3 cup sugar, evaporated milk, and margarine together in a saucepan; bring to a boil. Stir 1/2 cup sugar mixture into egg yolks until egg yolks are warmed. Stir egg yolk mixture back into saucepan with sugar mixture; bring to a boil and cook, stirring often, until reduced and thickened, at least 7 minutes. Pour hot mixture over cake. Set cake aside to cool until set, at least 4 hours.