Heat diced beef suet in a large Dutch oven over low heat until crisp. Remove beef suet and discard; reserve beef suet drippings in Dutch oven. Add chopped onion and minced garlic; sauté until tender. Remove onion and garlic with a slotted spoon, and set aside. Reserve drippings in Dutch oven.
Combine 1/4 cup flour, salt, and pepper; dredge roast in flour mixture. Brown roast on all sides in reserved drippings. Set Dutch oven aside.
Combine tomatoes, vinegar, mustard, and 2 cups water; mix well. Pour tomato mixture over roast in Dutch oven. Cover and simmer 2 1/2 hours or until meat is tender.
Cook macaroni according to package directions; drain and set aside.
Remove roast to a serving platter, and keep warm; reserve tomato mixture in Dutch oven.
Combine 2 tablespoons flour and remaining 1 cup water, stirring until smooth. Add flour mixture to tomato mixture; cook, stirring constantly, until mixture is thickened and bubbly. Add reserved onion, garlic, and cooked macaroni to tomato gravy; heat thoroughly.
Cut roast into serving pieces; serve with hot macaroni sauce.