Pictures would have helped a lot. But still, there are two easy to apply things that can help increase the wheel travel.
1. Add U Type clamps replacing rivets & 'pressed' rebound clamps
Riveted & pressed clamped system is good for high speed travel
2. Rearrange (by replacing, removing, cutting or adding) the leaf springs in such a way that the steps are longer. Meaning, there is more gap from where one leaf ends to the end of next in line.
Will additional body lift due to added leaves, appropriately longer shocks will also be required to avail that additional drop in diffs. during articulation.