One day ahead place 8 slices of bread (remove crust with electric knife) in bottom of a casserole with 4 slices of cheese, ham, pork, and the other 4 slices of cheese on top. Add sliced pickles. Top with remaining 8 slices bread. Beat eggs, milk, salt, pepper, and mustard powder together. Pour over sandwiches. Refrigerate covered overnight. Remove from refrigerator 1/2 hour before baking.
Preheat oven to 350 degrees F.
Mix cereal and melted butter. Spread over sandwiches. Bake for 1 hour.