Preheat oven to 350°. In a large bowl, cream the shortening, syrup and sugar until light and fluffy, 5-7 minutes. Beat in the eggs, milk and vanilla. Combine the flour, baking powder and salt; add to creamed mixture and mix well. Remove half the batter to another bowl., Combine melted chocolate and pecans; stir into 1 bowl of batter. Spread into a greased 13x9-in. baking pan. Add coconut to remaining batter. Spread carefully over chocolate batter. , Bake until a toothpick inserted in the center comes out clean, about 25 minutes. Cool completely on a wire rack., For frosting, in a small bowl, beat butter until smooth. Gradually add the confectioners' sugar and cocoa. Gradually add syrup, beating until smooth. Fold in marshmallows. Frost bars.