Make the crusts: Preheat oven to 350 degrees. Mix graham cracker crumbs, butter, sugar, and salt in a small bowl. Spread mixture evenly in a rimmed baking sheet, and bake until golden brown, 8 to 10 minutes. Let cool.
Press 3 tablespoons graham mixture firmly into eight 6-ounce glasses. Refrigerate until ready to use.
Make the curd: Prepare an ice-water bath. Whisk eggs, 3 yolks, and 1/2 cup sugar in a medium bowl; discard remaining yolk, or reserve for another use. Add lemon zest and juice, and salt. Set bowl over a pan of simmering water, and cook, whisking occasionally, until mixture thickens, about 5 minutes. Remove from heat, and whisk in butter. Strain through a sieve into a medium bowl, then set in ice-water bath, stirring often, until cold.
Bring corn syrup, water, and remaining 3/4 cup sugar to a boil in a small saucepan, stirring until sugar dissolves. Cook, undisturbed, until syrup registers 248 degrees on a candy thermometer. Wash sides of pan with a wet pastry brush to prevent sugar crystals from forming.
Meanwhile, whisk 4 whites with a mixer on medium speed until soft peaks form. Reduce speed to low, and pour hot syrup down side of bowl in a slow, steady stream. Increase speed to high, and whisk until stiff peaks form and mixture is no longer steaming, about 3 minutes. Add a third of meringue to chilled lemon curd, and whisk until smooth. Fold in remaining meringue in 2 additions.
Transfer lemon mixture to a pastry bag fitted with a 1-inch plain round tip. Pipe on top of graham cracker crust, filling to rim. Freeze until filling firms slightly, about 1 hour. Spoon Italian meringue into a pastry bag fitted with a 1-inch round plain tip, and pipe into each glass, covering evenly and swirling into a peak.
Hold a small handheld kitchen torch at a 90-degree angle 3 to 4 inches from surface of meringue. Move flame back and forth until meringue starts to brown. Alternatively, heat oven to 500 degrees. Place glasses on a baking sheet, and bake on top rack until meringue begins to brown, about 2 minutes. Serve immediately.
Use glasses that can withstand hot and cold temperatures. To ensure the towering desserts retain their loft even after freezing, gently fold the meringue into the curd in portions, not all at once.