Hi Chris 28, Buzz here. Among other things at work i teach an ETOPS class for other mechanics.
How can a "Thunder Guppy" become ETOPS? well, first you fly it more than an hour from any airport you can land at. According to the FAR's you're in ETOPS territory then.
Besides, how could they get 737's out to the Islands unless they had the range? UAL's original batch of 737's would only carry a few hours of fuel, small center bladder tank (or 2 ). Later they made the center tank integral which tripled it's fuel capacity. I hear rumor of a cargo pit fuel tank also, we had some 727's with them installed.
But you have do carry more than just extra fuel and a couple more radios. You have to have your maintenance program set up to track the oil consumption, and have a way to prevent easy mistakes from causing in flight emergencies. And then there are critical systems that get different treatment after you fix them.
Most of our ETOPS diversions are coused by sick passengers. Maybe we should give them a once-over inspection before they get to fly? (grin)