Seems there are no ready-made lowering kits at this time.
My investigation indicates that we can probably use BellTech 91-96 Dakota drop spindles to get 2" and then add lowering springs (or cut yours) and get another 2". Some grinding will be required. Lowering the rear is pretty straightforward as flipping the axle should get you 5" easy. However none of this is for amateurs as there will be additional issues.
I contacted a specialist and will update when I have more info. In the meantime, check out forums dedicated to lowering vans.