Would love to hear more about the cut away van tank usage and retrofit. Might be a good alternative for extended range and not having to shorten the stock tank for 4wd conversions.
I think it is a great alternative to shortening the stock tank but it doesn't come "bolt on" easy unfortunately.
The cutaways have a few different tank configurations but the most popular I've seen are the 40 gallon and 55 gallon aft-of axle tanks. I haven't measured out a RB van so I don't know if the 55 gal tank would fit in the space under there but it fits with room to spare under an EB. I've seen them advertised for ~$500 used to $1000 new, not including the sending unit. They're out there in plentiful supply though.
Two of the rear cross members in the frame have to be removed and replaced. I welded a tube between the frame horns before I cut out the cross members because the frame will likely move around/twist a bit once you pop the rivets out. Speaking of rivets... I used a heavy duty air chisel to break off the rivets. It worked well but took some time. I didn't want to risk cutting into the frame with a torch or plasma.
The tank is mounted between the frame rails with the support straps directly bolted to the bottom of the frame on one side and the other side bolted to a bracket running between the new cross members. A google search can turn up several pictures of these tanks sitting between the frame rails.
The filler neck comes out in an inconvenient spot (close to the rear A/C) and I'm not 100% sure how this will play out yet. I might have room to snake around the A/C lines and put in a new filler door at the back of the van. Worst case I'll spin the tank 180 and put the filler out the passenger side...or weld in a new filler tube in the spot I want it. This is probably the biggest challenge to using one of these tanks.
The fuel lines aren't anything special and the extended sections could be purchased from Ford or made from scratch with aftermarket hose/fittings.
The fuel level sensor works the same as a stock tank but I haven't hooked it up yet to see if the gauge on the dash reads right through the whole sweep.
Not exactly a bolt-in mod but still doable if you want the large capacity. It also opens up a ton of room for stuff along the frame where the stock tank was. Or if you really wanted, you could have two fuel tanks in the van.