All Caprice/Impala rear springs should be "pigtailed" at both ends. Meaning the spring is larger diameter in the middle, and winds down to a smaller diameter at both ends, which should be the same.
Take a pic of the rear springs you are planning on installing if you can. I'm a little confused by what you're asking exactly.
If you got them used, it's possible somebody cut one of the pigtailed ends off to have it ride even lower. In that case, put the big end up, and make sure it sits around the nipple thing on the frame.
It's not generally recommended to cut rear springs, but I cut mine and been running them hard for over a year with no issues. They can fall out when you jack the car up, or get airborne, so keep that in mind and be careful! Haha