Obvious stand-in double for Ernest Borgnine's character McHale, when early in the story there is a full-frontal shot of McHale when he hugs his cousin Giuseppe, played by Ernest Borgnine in that scene. The stand-in is heavier set with different facial features.
Near the end after they have used the split screen to show Borgnine in the same frame, moments later they show the one posing as McHale on the PT boat waving. They are still using the split screen cause all the action in the right frame stops while the left continues.