Relocated fuel tank question

[Kiwi]

I have a 1971 C-10 with the traditional fuel tank mounted just behind the front seat. I would like to remove the stock tank and replace it with some type of under-bed fuel tank.

Unfortunately I can not use the most common type of aftermarket fuel tank that mounts at the rear of the bed in-between the frame rails as:

1. I already have an aftermarket trailer hitch that hides in that area.

2. In the summers I install a vintage Alaskan pop-up camper in the bed which would make it nearly impossible to fill up the fuel tank (as the gas cap is usually on top of the bed or mounted in an area of the bed side).

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My dad bought new a 1971 Cheyenne that had an optional fuel tank located on the underside of the front left portion of the bed (just rearward of the driver). I don't remember if the tank was installed from the factory or installed by the dealer … but it definitely wasn't installed after leaving the dealership.

Questions:

1. Does anyone know if this tank was factory or dealer installed?
2. What was the size (in gallons) of the auxiliary fuel tank?
3. Does anyone reproduce the tank, mounting straps, and fuel filler hose assembly?
4. Does anyone reproduce a similar tank that is larger capacity than the original side tank?