Rank: I've got a '80's chevy LWB 4x4 in the garage I'm doing just that to right now... lowered the solid hangers for the rear spings about 4", re-braced with brackets for the new locations, shackle flip/drop hangers in the back, stock shackles, and stock springs to get about 8-10" lift, with a good pinion angle.... it's amazing what you can come up with in the garage with a welder and some buddies and some beers. Nice thing is that I still felt good about it the next day..... We're using 8" lift springs in the front with 2" longer shackles.
411: I would guess the combo of adding an extra leaf from another spring pack, say from a junk yard truck of the same design (AKA '99 to '04 with the leafspring front) and using slightly longer shackles would get you the lift you want, and at lower dollars. Might ride a little rougher than something you spend more money on, but it's up to you, spend more money, or more of your own time? Like Rankroddin said, longer shackles can affect the way your truck's steering works, and how the truck handles. That's not to say don't do it, just be reasonable... IMO, if the orig shackle was 5", going to 7" probly won't do much to the way the truck drives. More than that, you're pushing it. (Unless you're like some of my friends, I've seen some off-road only trucks with 10-12" long shackles! YIKES!)
Greg