Combine evaporated milk, milk, sugar, 1/2 cup water, flour, and egg yolks in a tempered glass bowl (such as Pyrex(R)).
Fill a large bowl with ice water, creating an ice bath.
Place milk mixture in a large saucepan of boiling water; cook, whisking constantly, until custard thickens and reaches a temperature of 170 degrees F (77 degrees C), 10 to 15 minutes. Transfer bowl to ice bath to cool the custard.
Mix 1 1/4 cup water, 1 cup heavy syrup from fruit cocktail, gelatin, and lemon juice together in a separate saucepan over medium heat; cook and stir until gelatin dissolves, 10 to 12 minutes. Refrigerate gelatin mixture until cooled, about 30 minutes.
Layer ladyfingers in the bottom of a deep 9x13-inch dish; top with a custard layer and fruit cocktail layer. Repeat layering with remaining ingredients, ending with gelatin mixture covering the last fruit layer. Refrigerate until set, 8 hours to overnight.