If using 4" zucchini, halve lengthwise. If using 8" zucchini, halve crosswise, then quarter lengthwise. Place in a large bowl. Add 2 tablespoons salt and 4 cups ice. Add cold water to cover. Top with a plate to keep submerged. Let sit for 2 hours. Drain; rinse. Divide dill sprigs and next 6 ingredients between 2 clean, hot 1-quart jars; set aside. Bring vinegar, sugar, remaining 2 tablespoons salt, and 1 1/4 cups water to a boil in a large saucepan. Working in batches, add zucchini and cook, stirring occasionally, until khaki in color and slightly pliable, about 2 minutes. Using tongs, transfer zucchini to jars. Divide hot syrup between jars to cover zucchini, leaving 1/2" space on top. Wipe rims, seal, and process in a boiling water bath for 10 minutes. Allow at least a week to pickle before eating.