I am in the planning stage of converting my wagon to wvo.
I have decided to remove the vacuum resevoir behind the main fuel tank and relocate a smaller one and most likely add an auxilary vacuum pump from a newer model to run the door locks. I have measured and believe I can fit a 8.5 gallon custom tank in it's place. I considered the space your thinking of but I dedcided to keep the fuel out side of the passenger space. I will be running vo in the stock tank and putting diesel in the new one. My advice would be to make a cardboard and tape mockup of the tank you want and use it as a template to weld one up. If you need to have it welded for you, you could have the welder coppy the final mockup. I am slowly moving forward with the conversion but would love to keep up to date on yours. In the off chance I finish my tank soon I will let you know and post some pics. Right now I am torn between using steel or aluminum and trying to figure out fuel gauge sending units, fuel line fittings and baffles to keep the sloshing down. good luck and let us know.