I ordered my new replacement springs from Jim Carters
http://www.oldchevytrucks.biz/47_55/full.asp?page=118At only about 100$ each I thought that was a good. Since your springs are shot I would replace them with new. I also added two short leafs from my old springs. This should raise the vehicle "two leaf widths" without stiffening the ride. I also ordered a replacement center bolt, which is excesive long, to account for more leafs, then trim off un-needed length. I purchased the poly liners but never used it. I didn't want to completely dissasemble the my brand new springs.
See in picture how last two leafs are doubled and centerbolt needs triming
http://good-times.webshots.com/photo/2448427800100505384SmDfISUnfortunately I can not tell you about the ride quality since truck isnt drivable yet.
But for the cost I would start by replacing those old springs and then go from there.