To remove any wax from the lemon rinds, cover the lemons in a tub of water with the vinegar and let soak for 5 to 10 minutes; rinse well.
In a sealable container, combine 61/3 cups water with the alcohol.
Using a vegetable peeler, remove the lemon zest in strips, leaving the white pith behind; add to the alcohol mixture (the strips should be fully submerged). Cover and let steep in a dark place until the strips of zest lose most of their color and the flavor is infused, about 1 month.
Strain the liquid, discarding the lemon zest. Add the simple syrup. Transfer the limoncello to a container and store in the freezer. Serve chilled, straight up.