[Marshall V. Daut]

As "inex01" recommends, if the spring needs servicing, now is a good time to take care of that. Unless your car has been restored in the last few years and you know for a fact that the spring leave ends have been ground at a bevel on the bottom and that lubrication still exists between the leaves, there will be no better opportunity to perform these tasks than when you install the Mitchell overdrive. You can also spread a layer of chassis grease on the top leaf and along the sides of the ones below it
before re-installing. This will reduce squeaking and metal-to-metal rubbing.
Contrary to what you often read here, I have always dropped the rear end WITH the spring still attached - for the past 50 years. I know there will be howls of derision about how dangerous this is. But I always attach a large C-clamp over the spring in the center as soon as it clears the cross member. The clamp stays in place as a spring spreader does its job prior to removing the spring from the rear axle. Once the spring is relaxed by backing off the spreader and laid on its side, the center bolt removed and then the C-clamp comes off. Leave the spring clamps in place while doing this to reduce the tension between the springs. Remove the two clamps after the center bolt has been removed. The spring can then safely be disassembled and serviced. Use a new high quality center bolt, not something purchased at the hardware store! And ensure that the head is squared up so that it will fit into the square hole in the top of the rear cross member. Put the C-clamp back in place until the rear end assembly is about to be re-installed into the chassis. The clamp is then removed and the assembly is jacked up into place. Piece of cake!
Why do it this way? I have helped friends try to install a loose rear spring back into the rear cross member because they read that was the "way" to do it. I decided long ago after helping them that this was more painful, frustrating and potentially more dangerous than the way I have described. That spring is heavy and awkward. You need two people to install the spring this way, while installing the spring attached to the rear end requires only one person. I have done it dozens and dozens of times with no injury. The key is use that large C-clamp during removal and installation. Because you are dealing with an old center bolt during removal, that is the time when it is potentially more dangerous than when re-installing with a new hardened center spring bolt installed. But for safety's sake, use the C-clamp anyway.
Once you have done the procedure as I describe, you'll never want to fight a loose spring re-installation again.
Marshall