I didn't mean the rear shackles. they have big brackets on both side welded to the housing to adjust height and roller brackets bolted to the springs so the housing moves back and forth so the two suspensions don't bind. you just need enough spring to hold the hotrod up and you adjust height as mentioned, no need to do anything to the springs. use the stock rear shackle as this set-up can get plenty of rear body raise. you will be trying to get 5"-6" to hook good. in the front use a 90-10 shock to get it up to it's fullest.
you may have to really search for the ones with the big roller on the net. I found several other type with the adjustable height brackets but not the one with big roller.