In the one scene near the end, the PT boat was seen heavily bow-down in the water. With 20+ people on the bow of a boat of that size, there would be too much weight on that area, and the bow would go down in the water, and the stern would go up. This shows that the boat used for these shots was one of the rescue launches modified to look like a PT boat.
Peggy Mondo, who played Mama Giovanni in this and other Italian-themed episodes, also played Little Flower, the daughter of the Chief, in some of the episodes with the South Pacific theme two seasons earlier.