Into a large bowl, sift together 1 cup of the confectioners' sugar, the cocoa powder and allspice. Stir in the rum and corn syrup. Stir in the vanilla wafers and walnuts, and mix well. Place in the refrigerator to firm up slightly, about 30 minutes. (The mixture may appear crumbly and dry; this is O.K.)
Place the remaining 1/2 cup confectioners' sugar in a shallow bowl or dish.
Using a tablespoon, scoop out portions of the chocolate mixture and press into 1-inch balls. Using your hands, roll the balls in the confectioners' sugar, coating evenly.
Place on a baking sheet, cover with plastic wrap and refrigerate overnight. Store in an airtight container in the refrigerator for up to 2 weeks, placing waxed paper between the layers to prevent sticking.