Spread 2/3 cup Thousand Island dressing on one side of 12 slices of bread; arrange 1 slice cheese, 2 teaspoons sauerkraut, and 2 slices corned beef evenly over each slice. Stack to make six (2-layer) sandwiches spread remaining 1/3 cup dressing on remaining 6 bread slices, and invert on top of sandwiches. Spread butter on outside of top slice of bread; invert sandwiches onto a hot skillet or griddle. Cook until bread is golden. Spread butter on un-grilled side of sandwiches; carefully turn, and cook until bread is golden and cheese is slightly melted. Secure sandwiches with wooden picks; cut crosswise into thirds. Serve hot.