In a very large, deep skillet, heat the remaining 1/4 cup of olive oil. Add the chorizo and cook over high heat, stirring occasionally, until the fat is rendered, about 2 minutes. Add the shallot and garlic and cook until fragrant, about 1 minute. Add the tomatoes, clams and clam juice, cover and cook until the clams just begin to open, about 5 minutes. Add the mussels, cover and cook until all the shells have opened, about 3 minutes. Stir in the shrimp, season with salt and cook until pink and curled, about 2 minutes.