Actually...a reverse bend in the leafs at the shackles is totally normal. Overloaded or not. Many of us have this same issue and it results in a net loss of 1.5"-2" of rear ride-height. If you've leveled your H3 by raising the front...the sag is even more noticable, due to the extra weight shifted rearward. The H3 has a very delicate front-to-rear balance, and it doesn't take much change to feel a difference in handling.
So far, I think Speedy has the best fix. He grabbed a pair of junkyard leaf packs from a 2500 Chevy truck...took them apart...and inserted the longest leaf into the H3's spring pack. He installed it into the 2nd position, right up against the main leaf of the H3. This is a much better idea than a traditional add-a-leaf which gets installed in the overload position (lower in the stack). The traditional add-a-leafs don't do much to support the main leaf near the spring eye, which seems to be where the problem is.
Another nice thing about this mod is that the full-size Chevy springs are drilled off-center, just like the H3's springs. You'll find that any standard add-a-leaf you buy will have the hole equal distance from either end...and that doesn't really work with the H3. I'm currently running ebay add-a-leafs and I re-drilled mine to position them correctly with the rest of the springs. Trust me...you don't want to drill spring steel!!! They work good but, the next time I have stuff apart...I plan to swap-in some Speedy springs.
P.S. Notice how your leaves seem to be "de-laminated" near the clamp? They should be pressed together nice & tight, and you can clearly see how the main leaf has gone flat, while the ones below it still have their arch. That's the problem you need to fix! Adding the full-size second leaf helps this tremendously...plus you can tighten up that clamp when you put it back together. Maybe even add additional clamps?
