The Rolex GMT Master that Magnum inherited from his father wasn't introduced by Rolex until 1954, after his father was shot down during the Korean War.
Featured are several close up shots of the Rolex GMT Master that Magnum is wearing. Each shot shows a different model/version of the watch. It looks like the shots were used to determine which watch looks the best. They settled on the "Pepsi" Rolex, one that has a red/blue bezel and black face.
While Rick is talking to Sandy about setting the anchor, you can see a large rocky island in the background which is the same rocky island just offshore from Robin's Nest. Rick is only a few hundred yards from shore.