Before you pay $300 to narrow a rear end, you might shop around for a alternate rear. Is this 3/4-ton van a G-20 with 5-lug wheels?
If so, it appears the brake drums and backing plates are different than the 1/2-ton pickup version, but at least on the one I had the rear itself, aside from being wider, is the same.
Also, I've been told the rotors are the same part number as those used on a same year 1/2-ton pickup.
Some guys are running the front IFS from a pickup under AD pickups. Its really too wide, but with offset wheels can be made to work. Since the crossmember on the van is not an unbolt operation, like those on pickups, I'd suggest looking for 1/2-ton pickup stuff and upgrading the brakes and springs to the 3/4 spec.
One more thought. The van power steering is much harder to adapt to your truck than a pickup type would be.
I've been considering a similar approach on one of mine. I parted out a van and learned a lot about those parts in the process. If I take this approach it will be based on pickup parts, not van parts.
