Cook jumbo shells according to package instructions, until al-dente. Drain from water and lay out on a large dish to cool, so that they don't stick together.
Meanwhile, brown ground beef and sausage in a large skillet over medium heat. Remove grease.
Add cooked meat to a large mixing bowl. Add chopped bell pepper, onion, parmesan cheese, oregano, garlic, olives, and 1/2 cup of marinara sauce. Season with salt and pepper, to taste.
Preheat oven to 350 degrees F.
Spread a thin layer of sauce over the bottom of a 9x13'' or similar size pan.
Add a heaping spoonful of meat mixture into each jumbo shell, filling them very full, and line them up along the bottom of a 9x13'' or similar size pan.
Spoon remaining sauce evenly over the noodles. Top with chopped pepperoni's and mozzarella cheese.
Bake in preheated oven for 25-30 minutes or until cheese is melted and bubbly.