They can give you 3+ inches of lift depending on how long of shackle you use, I used chevy drop shackles connected to my stock toyota shackles...
I don't see how "junkyard springs" are any different than the springs you run on your truck everyday, unless they are bent or damaged from being wrecked or something...
Just do it. Do it.
The info is in my build thread here:
http://board.marlincrawler.com/index.php?topic=39009.0
