For Thousand Island Dressing, in a medium bowl, combine mayonnaise, sour cream, green pepper, chili sauce, and green onion, regular onion or onion powder. Carefully fold in the chopped egg and pimiento, if you like.
Stir drained sauerkraut into dressing. Set aside.
On 4 slices of rye bread, arrange 4 slices of corned beef on each bread slice. Spread sauerkraut mixture over corned beef. Top each with 2 slices cheese. Place the remaining bread slices on top of cheese. Spread tops with softened butter.
Brush a grill, griddle or large, heavy skillet with butter. Place the sandwiches, buttered side up, on grill or griddle. (It may be necessary to cook two sandwiches at a time if the grill is too small.) With a spatula, press the sandwich tops. Cook over medium-low heat for 5 to 6 minutes or until the bread is toasted and cheese is melted, turning sandwiches once. Makes 4 servings.