Lowering 2 inches w/o lowering tow capacity

I'm blown away by the wise and thoughtful responses from you guys. Wow. Thank you.

It looks like airbags would cost around $700-$800. I imagine replacing shackles would be less, but I don't know how much. I'll look into it.

If the shackles are in tension, longer shackles will lower the van, effecting little else. If the axle is under the spring, and there is clearance in the wheel wells, moving the axle above the spring would lower the rear the height of the axle + the height of the spring pack. A third option would be pulling some leafs out and replacing them with airbags.

If its a frame garage, it may be cheaper to make the garage door taller

Your proposed method will not work on the E-series. There are no lift blocks, and the shackles are already underslung.

What might get you enough drop is removing the lowest leaf spring, aka the "overload" spring. You then restore the spring capacity with a Firestone airbag kit.

Or, you can do full air-ride, but that might cost more than a bigger garage door.
http://dallassmithcorp.com

Don't know about the van, but on the F350 trucks you can replace the 4" blocks under the springs with 2" blocks. Had that done on a previous 2007 F350. May be the same on the vans.

Rear suspension is easy enough to lower, you can remove the 350 spring block and put in a 250 spring block, or even a smaller block, you can get the springs re-arched, different things can be done. The front is harder. You have the twin I-beam suspension on the E350, lowering it will change the camber, you will probably have issues with the bump stops, etc. I have read of modified I-beams that accommodate those issues.

Unfortunately, you're pretty much stuck with the stock tires or bigger to have the weight capacity for hauling and towing. The smaller and lower a tire gets, the less weight capacity it has.

You need more than 0 inches clearance to get the van in the door. That's something you might want to consider if you haven't already.

Another issue is, a van is not exactly a truck. It's enough different that the lowering kits you can purchase commercially may or may not fit, or may or may not give you the height difference you need.

Auto manufacturers just don't see enough of the "big family, big trailer" crowd to make it profitable to produce a vehicle that's suitable for both hauling a big family and towing the big trailer it takes to house them.