Not sure if this is the correct forum for question, so move if needed...
I'm also not why it took me this long to realize that the gas tank that I've had in my 59 3804 is from a 60-66 truck. I have had the tank out to clean it and put in a new fuel sending unit, and was getting confused why my tank didn't have the vent pipe as on other 55-59 tanks. Thought it might be an aftermarket tank. Never completely compared mine to a 55-59 as it never crossed my mind that it'd be from a different style truck. Finally saw a 60-66 tank today on Jim Carter site and, bingo, saw the difference and matched mine up to the newer years. Good thing I did before ordering a 55-59 sending unit, as that wouldn't have fit.
Truck is Canadian built, so not sure if that would have anything to do with the different tank showing up. I just figure that the PO used whatever was handy. Other than losing a point or two at Pebble Beach Concours for an unoriginal tank, it's worked this long so it's going back into the truck. I'm sure this isn't the oddest thing but thought I'd share. Truck doesn't care where the gas is coming from as long as I keep it fed.