The usual method is to weld a piece of 2x2 square tubing from one spring hanger to the other directly across, above the bolt holes in the hanger and close to the frame. This would transfer any stress to the other side when backing to balance the forces of twisting to both hangers instead of just the one. To be honest you may not need to do anything unless you can see some evidence of excessive flexing while backing.
From your photo's it appears that they used over sized spring hangers and had to pinch them together to fit your springs inside. I also see that a few of your shackle bolts are not pulled down to the shackle all the way. You might want to check those.
Walter and Janie Rogers
2012 Sundance 277RL
TV 2006 Silverado 2500 6.0