Preheat the oven to 350°F (175°C). Cook the jumbo shells in a large pot of boiling salted water according to package directions until al dente; drain and set aside.
In a large skillet over medium-high heat, cook the ground beef until no longer pink, breaking it up with a spatula; drain any excess grease.
Add the taco seasoning and cream cheese to the hot beef and stir until the cream cheese melts and the mixture is well combined.
Stir in the drained corn and rinsed black beans with the beef mixture until evenly distributed.
Spread the salsa in an even layer on the bottom of a 13x9x2-inch baking dish.
Spoon a portion of the meat mixture into each cooked shell and arrange the stuffed shells on top of the salsa in the baking dish.
Pour the taco sauce evenly over the shells, cover the dish with aluminum foil, and bake for 30 minutes.
Remove the foil and sprinkle the Monterey Jack and cheddar cheeses evenly over the shells. Return to the oven and bake uncovered for 10 minutes, or until the cheese is melted.
Top with green onions, sour cream, olives, and diced tomatoes as desired, then serve.
