Whisk together flour, allspice, and salt in a small bowl; set aside.
Melt molasses and butter in a small saucepan over low heat. Remove from heat; let cool slightly. Stir in bourbon. Transfer to a medium bowl; whisk in sugar until smooth. Stir in flour mixture and 1 cup pecans. Refrigerate dough until firm, at least 1 hour or up to overnight.
Preheat oven to 400 degrees. Scoop balls of dough using a 11/4-inch (1 ounce) ice cream scoop; roll in remaining 3 cups pecans. Space 1 1/2 inches apart on baking sheets lined with parchment paper. Bake until flattened and lightly colored on edges, 9 to 11 minutes. Let cool on sheets 3 minutes. Transfer to wire racks; let cool completely.
Store in airtight containers at room temperature up to 1 week.