Toast the bread in a roomy heavy skillet over low heat with 2 tablespoons butter and 2 tablespoons olive oil, stirring frequently for about 15 minutes, then transfer it to a large bowl to cool and keep the skillet unwashed. Look for golden edges, a crisp surface, and a warm, nutty aroma.
Boil the jumbo shells according to the package directions for pasta served with sauce while the bread cooks, then drain gently and set aside. The shells should feel tender and flexible enough to open without splitting.
Set the oven to 350°F. The assembled shells will need a short warming bake rather than prolonged cooking.
Return the skillet to medium heat with the remaining butter and olive oil, then stir in the garlic for about 1 minute. Stop short of any browning; the garlic should smell fragrant and remain pale.
Pour in the wine and add the salt, black pepper, and crushed red pepper flakes, allowing the mixture to simmer for about 2 minutes. The liquid should reduce slightly while remaining plentiful enough to form a sauce.
Sauté the chopped shrimp in the sauce for about 2 minutes, take the skillet off the burner immediately when they turn pink, and stir in the lemon juice after slight cooling. The shrimp should have just changed color rather than tightened into firm, chewy pieces.
Lift the shrimp and garlic into the bread bowl with a slotted spoon, then mix in 2 tablespoons pan liquid, all but 2 tablespoons cheese, and all but 1 tablespoon parsley before tasting and adjusting the seasoning. The filling should hold together loosely, with moistened bread cubes and distinct pieces of shrimp.
Fill 8 to 10 shells evenly and arrange them in an ovenproof dish that holds them comfortably, then spoon a little sauce over each, pour the remaining liquid around their bases, and scatter the reserved cheese on top. The bottoms should sit in sauce rather than against a dry baking dish.
Bake for about 10 minutes until warm throughout, allowing longer for refrigerated shells, then spoon the hot pan juices over each shell and finish with the reserved parsley. The centers should be warm and the pasta edges moist, without waiting for a deeply browned top.