Step 1: Heat a nonstick skillet over medium heat. Add the sausage and fry it until lightly browned and crumbly, breaking it up with the edge of a wooden spoon, about 5 minutes. Transfer the cooked sausage to a strainer to drain. Discard the fat from the pan.
Step 2: Heat the olive oil in the skillet over medium heat. Add the scallions, red pepper, parsley, garlic, and lemon zest and cook until lightly browned, 3 to 5 minutes. Stir in the bread crumbs and sauté until lightly browned, 3 minutes. Stir in the cooked sausage and Sambuca. Correct the seasoning, adding salt and pepper to taste; the mixture should be highly seasoned. The recipe can be prepared to this stage up to a day ahead and refrigerated, covered.
Step 3: Scrub the clams with a stiff brush under cold running water to remove any grit. Discard any clams with cracked shells or shells that fail to close when tapped.
Step 4: Just before serving, set up you grill for direct grilling and preheat to high.
Step 5: Shuck the clams, working over a bowl to catch the juices. Discard the top shell. Place the clams on the shellfish rack. Place a spoonful of stuffing on each clam.
Step 6: When ready to cook, place the clams in their rack on the hot grate (or arrange the clams directly on the grate, positioning them so that the bars hold the shells level). Cover the grill and cook the clams until the juices bubble and the shellfish are just cooked through, 3 to 5 minutes. When done, the clams will be slightly opaque and firm to the touch. Transfer the grilled clams to a platter or plates, taking care not to spill the juices. Serve at once, with lemon wedges for squeezing.