Remove the "tube nut" completely. Then you can remove the "connector". Give it a good cleaning and thread it into the new radiator. I use some Teflon tape where it threads into the radiator, it's NPT if I remember correctly and SHOULD seal without anything on it though.
Okay got it. Just thinking it out. My lines are metal, so not much bending back will happen once i loosen the "tube nut" or will it give me an inch or so of movement?