Inside the little bell at the end of the line there is a quick connect fitting, you need a release tool to remove it. Not sure what the nut is at the end of the line, it would make it impossible to use the release tool if it cannot be moved.
The nut came off where the fitting actually enters the radiator. It's only resting on the bell housing you refer to. The new radiator came with the following pictured fittings. I'm thinking I either get a new line that matches the hardline connection on the tranny end and the new fitting or I cut the line and use a barb fitting.