Mine are up for sale. One has to go, I don't need both. Located in Chippewa Falls, WI. The Quigley 4x4 V10: https://eauclaire.craigslist.org/cto/d/eau-claire-2012-ford-350-xlt-quigley-4x4/7071875460.html
The E-350 V10 XLT that wants to get converted...
How much are you seeing online? Last time I bought a single hinge, it was around 80-90 I think at the dealer. Granted with a discount, but not too bad. If you only do one and it's bolted on you can play with the alignment to get it straight.
Go to the GM dealer and get the replacement hinge kit. Comes with hinge and all bolts to do job. Your only issue would be paint. It's actually pretty easy to do. Drill out spot welds, bolt on new hinge.
Not sure if you're aware, but they sell complete replacement hinges for the GM side doors at the dealer. I think it was around $70 per hinge the last time I did one. You drill out the spot welds, and then simply bolt them on. Obviously have to paint, but then it's all brand new.
Check out the 2008-2010 Dodge Caravan or Chrysler Town and Country. There was a short-lived option called Swivel n Go for the second row. The seats would swivel around 180 degrees, had integrated belts, slides built in, and the whole thing was removable. I'm picking up a pair tomorrow for $150...
Here's one in Illinois. 2010 V10 EB conversion van. 25k miles, $20k
http://www.boblindsayhonda.com/used/Ford/2010-Ford-E-350SD-ed53c9720a0e0ae844812eb16521c157.htm