It might make a difference how early you want to go, but I'm sure they all interchange from 1964 up. That doesn't mean they're all the same. They're just all the same length & will all bolt into the car.
If you keep them complete and do them in pairs they will all interchange.....from '60-76. Even some Plymouths and DeSotos in the late '50's have springs the same dimensions. I would use the later 6 leaf ones if it were me.