Filling: Drain peaches, reserving 1/2 cup of syrup for the sauce. In a large mixing bowl, combine peaches, brown sugar, tapioca, cinnamon, lemon juice and vanilla. Mix gently, but well. Pour into an ungreased 11 x 7 baking dish. Set aside. Topping: In a second large mixing bowl, combine the flour, sugar, baking powder and salt. Cut in butter until mixture resembles coarse crumbs. Stir in lightly beaten eggs. Drop by spoonfuls onto peach mixture; with moistened fingers gently spread evenly. Bake at 350F for 50 / 55 minutes or until filling is bubbly and a toothpick inserted into the crust topping comes out clean. Let cool for 10 minutes before serving. Sauce: In a small saucepan, combine the brown sugar, flour, and salt; mix well. Add butter and reserved peach syrup. Stirring constantly, bring to a boil over medium heat; cook and stir for one minute or until thickened. Remove from heat and stir in lemon juice. Serve warm, over cobbler.