In a small bowl, stir together paprika, peppercorns, oregano, thyme, celery seed, salt, and red pepper.
In another small bowl, stir together mustard, onion, and garlic.
Rub the mustard mixture over the rib roast, but not the bones. Sprinkle spice mixture over the meat. Cover meat and chill in the refrigerator overnight.
Place the meat on a rack in a shallow roasting pan. Insert a meat thermometer. Roast in a 325 degree F oven for 1-1/2 to 2-3/4 hours or until the thermometer registers 160 degree F to 170 degree F. Cover the meat with foil for the last 15 minutes of roasting, if necessary, to prevent overbrowning.
Let meat stand, covered with the foil, for 15 minutes before carving. Carve meat and serve with Horseradish Sauce. Makes 10 to 12 servings.
In a bowl, stir together shredded radishes, prepared horseradish, dairy sour cream, Dijon-style mustard (if you like), and sugar. Whip whipping cream to soft peaks (tips curl). Fold whipped cream into horseradish mixture. Makes 2 cups.