fuel tank: found
I managed to find a fuel tank that will fit between the frame rail and the drive shaft under the front of the bed. It's from a mid-70's nissan pickup, and I found it at Blake's Small Car Wrecking in Erie, CO. I highly recommend them for finding odd parts - they have a complete computerized inventory of every part in their junkyard. The tank looks to be only about 10 gallons maximum, so I may try to get it to fit between the frame rail and the drive shaft on the driver's side, and find another tank to match on the passenger side, but that may involve moving the exhaust.