Grease two 9x5 loaf pans. Set aside until needed.
Cream together butter, 2 cups sugar, and eggs. Add milk, flour, and baking soda. Mix well.
Put 1/4 of batter in each greased loaf pan.
Mix the 2/3 cup sugar and cinnamon in separate bowl.
Sprinkle 3/4 of the cinnamon mixture on top of the batter in each pan. Add remaining batter to pans; sprinkle the remaining cinnamon topping. Swirl with a knife.
Bake at 350 degrees in a preheated oven for 45-50 minutes or until tester comes clean. [I had to bake them for 65 minutes before they were finished.]
Cool in pan for 20 minutes before removing from pan.