Spicy Pickled Shrimp

2 lbs Unpeeled, Large Raw Shrimp
3 Small White Onions (thinly sliced)
1/2 cup Olive Oil
1/4 Tarragon Vinegar
2 Tbsp Pickling Spices
2 tsp Salt
1 tsp Sugar
1 tsp Worchestershire Sauce
1/2 tsp Dry Mustard
1/4 tsp Ground Red Pepper
1/4 cup Chopped Fresh Parsley

Peel shrimp; devein, if desired. Cook shrimp in boiling water to cover 3 to 5 minutes or just until shrimp turn pink; drain. Rinse with cold water. Layer shrimp and onions in a large bowl. Whisk together oil and next 7 ingredients; pour over shrimp and onions. Cover and chill 24 hours, stirring occasionally. Stir in parsley just before serving.