[euromodder]

You could put vertical fences on the insides of the leaf springs.
The belly pan can then go a bit higher up between these fences.
The front of such a fence can form the inner line of a fairing that shields the rear wheel/spring ; the rear end can become part of a boattail for the wheel/spring.

The differential can go under a bulged streamlined fairing of its own.
Mind the vertical travel of the diff. , or eliminate that by attaching the aft belly pan to the rear axle.
In the later case, the belly pan will need somewhere to pivot and will need some play to make up for the vertical movement.