Score steaks diagonally on both sides.
Use tenderizer according to directions.
Spread one side of steaks with horseradish.
Combine onion, celery, butter, and seasoned salt; spread on steaks.
Roll up as for jelly roll.
Fasten with skewers and tie with string.
Insert spit rod through center of meat rolls.
Adjust holding forks; test balance.
Place medium coals on both sides of drip pan.
Attach spit; position drip pan under meat.
Turn on motor.
Grill over medium coals till done, about 45 minutes.
Let stand a few minutes; remove strings and skewers.
In small saucepan heat sour cream over low heat; do not boil.
Carefully carve meat rolls into thin slices and place on bread.
Spoon warm sour cream atop meat.