Not sure if it matters to you, but often the internationally configured planes on domestic routes will not have in flight wi-fi. You'll get a better seat, no wi-fi, and the same domestic F service and food.

Some people have been able to SDC for later legs of their flights at the 3 hour window of the first flight, but I think most agents will shut you down. You can just keep trying to call back. I wouldn't worry about the F/J inventory disappearing on those routes, as they usually save the upgrades for the gate and don't do them at the window. However if you'll be flying at the 3 hour window opening, that could be an issue and you can explain this to the phone agent.