Replacing the S spring on Door Hinge...possible?

Driver door on 66 ddart /6/ will not stay open. Lower hinge is missing the S spring. I have found another hinge, only it is for the Right side door. It has a good S Spring.
I see online that you can buy the S spring, so I assume it is possible to replace?

So #1: how can I remove the S spring from the wrong hinge.
#2: how can I put the S spring into the driver hinge? Does the hinge need to be removed from car?

I have a vice, safety goggles, I have lots of screw drivers and I have a hot Saturday afternoon to figure this out. Guys it is going to be over 100 deg here in sunny Southern California. Help me out please.