I've been running thru my head the amount of stuff you'd end up changing. IF-and its a real big IF-the lump will physically fit-and you can get around things like pan clearance-motor mounts-clearance to the body, off the top of my head to make a 7.3 work, you'll need : transmission
VSS (vehicle speed sensor) + possibly the tone ring on the ring gear. (you wont even get the bus to move without this right.)
Gas pedal (which will be different for a van/truck)
Dashboard (again-different van/truck)
a van specific ex. manifold-(can't remember which side)
a van left side valve cover-and oil filler tube
a van tranny dipstick.
The motor + even more so the tranny are VERY computer + sensor dependent.
The motor weighs 900 lbs-and the tranny 350. You need a serious cherry picker to get the motor out. And you can cut the radiator support to make more room. Its a crazy tight squeeze.