In a medium bowl, mix together ground beef, crushed crackers, onion, eggs, 3/4 cup ketchup, and 1/4 cup brown sugar until well blended. Process into 1 9x5-inch loaf pan. Lay the two slices of bacon over the top.
Bake for 1 hour in the preheated oven, or until cooked through. While the loaf bakes, mix together the remaining 1 cup ketchup, vinegar, salt, mustard and 1/2 cup brown sugar. Spread over the top of the meatloaf for the last 15 minutes of baking.