Perhaps somebody else (Jeff the Marmot?) that's had the springs out can comment..
Sorry I've had a very busy week, so I'm just getting back to this.
I've replaced the rear springs a few times while trying to fine tune the height, plus I've added different size pucks above them as a spacer with various springs, so you could say I've had the springs in and out a few times.
Assumption:
My 4Runner has 2-3" of lift, which could come into play with this process. If you don't have any lift, I'm not sure if you'll have enough room to flex the axle down to the ground with this method. I'm guessing it'll still work.
I try to be very cautious when I have anything lifted in the air. I'm big on safety.
You might have already dealt with this during the last week, but here's how I do it...
Step 1 - Put the vehicle in 4 wheel drive and drive it forward and back to make sure it's engaged. (And for someone like me who has front manual hubs, engage them). When you park it, pull the e-brake on hard. Even though the e-brake only effects the brakes on the rear wheels, the drivetrain in 4x4 also prevents the front wheels from turning. This makes it far less likely for the vehicle to move or fall off jacks when you're prying on it.
Step 2 - Disconnect both endlinks of the rear swaybar from the frame to allow the axle to articulate.
Step 3 - Disconnect the lower bolts of the shock mounts so the axle can fully extend. The top bolts of the shocks absolutely suck to deal with, so don't mess with them.
WARNING: Like Dan said, if you have a stock rear brake line (above the rear diff), it's extremely easy to reach its max extension and damage it. I have an aftermarket braided brake line there that's several inches longer than stock so I never have a concern about it.
Step 4 - Slightly raise the height of one side of the frame and set a fairly tall jack stand under the frame immediately forward of the frame's rear lower control arm mount. There's only something like 60% of the vehicle in front of this pivot, but it'll be OK. I have a couple of cheap harbor freight 6-ton jack stands for this purpose - not for the weight rating, but for the height and stability.
Step 5 - Remove the rear wheel on that same side as the jack stand. Keep the other rear wheel in place. This is where you need to carefully watch the brake line if yours is stock length. With the floor jack under that side of the axle, slowly set the drum brake on the ground or close to it.
Oh yeah - I have a 2" extension bracket where the e-brake cable is secured to the axle. If you don't have an extension there, you might need to temporarily disconnect the bracket from the axle. That's just left of the diff and to the right of the upper control arm "tower". It'll just flex easier when disconnected.
Step 6 - Replace spring on that side. I stand on the drum brake to flex it down a bit more if necessary. You're only flexing the rubber bushings in the 4 links + panhard. The right side of the axle will be more willing to flex further downward due to the panhard bar being connected to the left side of the axle. When you finish with that side, put the floor jack under the axle again on that side and slowly raise it while making sure the spring seats properly. Bolt that tire back on and set it on the ground.
Repeat for the other side.
Reconnect swaybar and shocks after you're done with the springs. It'll be sitting on all 4 wheels normally (and level) when you do that.
I guess the critical factor here is being able to have lots of flex while not worrying about the brake line. I honestly don't know if you could follow through with this process with a stock brake line even if you're careful with a floor jack under the diff.
What I like about this is the vehicle is close to its normal height and 3 wheels are always on the ground, so it's not going to just "fall". You're flexing the axle down instead of jacking everything way up in the air. The jack stand helps support that side of the vehicle and provides stability, but a majority of the vehicle weight is still on 3 wheels which don't want to move since it's in 4x4.
If for some reason you need to disconnect the panhard bar, you would need to remove all tension and weird torsional forces before messing with those bolts. It's not fun to reconnect it and I recommend you avoid disconnecting the panhard. But if you do mess with it, you'll probably need some hefty trailer ratchet straps to pull the axle and frame one way or the other in order to reconnect the bolt.