Rear Leaf Springs

[Averix]

Ok, I have an 84 1/2 ton 4x4 and am looking at lifting it up 4". I was looking into lift leafs and while taking a look at whats on there now, I noticed that the frame seems to have matching holes about 4" back of each of the bolts on the rear leaf hanger bracket.

Does this mean I could change to 56" springs? From my understanding the 56" springs are offset a little bit front to back so the axle position should stay the same. And if so, which would be the way to go? The truck will mostly be for hauling and towing.

Thanks in advance!