My next step with my impala was to lower the rear a little bit, to match the 2″ drop I gained up front with the dropped spindles.
The rear spring install is very straight forward. I basically raised the car up very high and supported it with jackstands. Then I put the jack under the rear end and lifted it until the the springs compressed a little. I unbolted the lower shock mounts, then loosened up the lower spring retainer cups. I then very carefully lowered the rear end back down.
At this point, I could finish removing the lower reatining cups and pull the springs out.
BTW, since my car is a Super Sport with a nice 327 that came standard, it received the optional 12 bolt rear end as opposed to the 10 bolt, which also means that is came with two upper control arms as opposed to the one. For a stock rear end, it is pretty beefy!
I set the springs next to each outer to see the difference, and my new ones were about one coil shorter.
I installed the springs just like the old ones came out. It was a very simple install, and as soon as the springs settle, should give me the exact stance I want.