Are you really set on getting s10 springs? Everything I've seen so far would suggest that 88 to 98 1/2 ton chevy rears or grand wagoneer springs are the ones you want for a rear setup.
The chevy's seem to give about 3" or 4" of lift and flex very well, they are a 3 leaf spring and are 63" in length. These spring are wider than the stock toy springs at 2.5" so new perches and shackles will be needed.
The waggy spring give about 3" to 4" of lift, flex very nicely, and are a little shorter then the chevies at 57" I think. These are either a 5 or a 7 leaf pack with the preference being the 7 leaf variaty, as the 5's are too soft. 350toy runs these on all four corners and his rig is looking sweet.
Both of these choices should be easy to find in a wrecking yard, the chevy would be easier to locate I think, and prices I've seen are around $100 to $200. I haven't looked for a set yet myself so they could be more.
As for a 3/4e setup the main leaf from a stock toy rear pack has been used by lots of people and seems to work very well. There are some on this board that are running this I think, a search should turn up some good answers.
Here are some links for you...
Chevy swap
Toy main 3/4e
Waggy info
More waggy info
BBP's waggy setup
I know it's a lot of info and none of it is on the s10 springs but this is what works really well and seems to be the hot setup. I think that the s10 swap is now sort of like the mazda swap and is kind of old school, I could be wrong here but this is my opinion. I plan on doing a front waggy with either rear chevy or waggy setup sometime around dec or jan and have been playing with the idea of a pinned 3/4e rear. Just remember that for every inch of shackle and hanger lift you add you will get a half inch of suspension lift.
Hope this helps.