For syrup: Combine sugar, lemon juice, and water in small saucepan. Bring to boil over medium heat, stirring until sugar dissolves. Reduce heat to medium-low and simmer 1 minute. Cover and chill.
For curd: Whisk eggs, sugar, and lemon juice in heavy medium saucepan to blend. Add butter and lemon peel. Stir over medium heat until curd thickens to pudding consistency, about 10 minutes. Transfer to small bowl. Press plastic wrap onto surface of curd. Chill until cold, at least 4 hours. (Can be made 3 days ahead.).
For fruit and topping: Combine 2 baskets raspberries and 1/4 cup sugar in bowl. Mash berries coarsely with fork. Let stand until juices form, stirring occasionally, about 30 minutes.
Cut cake crosswise into 8 pieces. Cut each piece into 3 strips. Line bottom of 3-quart trifle bowl with 8 cake strips, trimming to fit. Drizzle with 3 tablespoons syrup; spread with 2/3 cup curd, then half of mashed berries. Repeat layering. Top with remaining cake, syrup, and curd. Cover; chill overnight.
Beat cream and 3 tablespoons sugar in bowl until peaks form; spread over trifle. Mound remaining berries in center.