I'm going to go with Denny on this. New fittings are cheap. About the only real reason for trying to save an old one is if it's an odd size fitting that isn't available on the aftermarket. Later GMs are bad about that on the MC and Prop Valve.
If you do want to try to save them, the methods mentioned will work, however, I would use a 6 point socket rather that vise grips to hold it. Less change of damaging the hex. Also, run a thread chaser or die over the threads to clean them thouroughly.
