Preheat oven to 350°. Grease jellyroll pan.
Remove pork fat from pork & beans. In bowl, mash beans and pineapple. Add sugar, flour, baking soda, cinnamon, baking powder, salt, oil, and eggs. Mix well. Pour into prepared pan. Bake for 25 minutes or until bars test done. Cool completely.
In saucepan, combine sugar, milk, and butter. Bring to a boil. Boil for 1 minute. Remove from heat. Add butterscotch chips. Stir until melted. Spread over cooled bars while frosting is still warm and thin.