1980 - 86 FORD TRUCKS:
          FUEL SYSTEMS
                    AIR CLEANERS
                    CARBURETORS, CHOKES, & EFI
                    FUEL SYSTEM ILLUSTRATIONS
                    FUEL SYSTEM PART #'S

The 1980 to 86 era was a time of significant change on the fuel systems for these trucks.  In the early years they were all carbureted, but by the end there were EFI systems, which required in-tank fuel pumps.  Further, the 460's had a problem where the fuel got hot and vaporized, so they added in-tank pumps and a hot-fuel handling modification to those trucks.  But, the in-tank pumps are larger in diameter than the sending units that went in the early tanks, so the later tanks had a larger diameter hole in them for the pumps.  Obviously the larger hole in the tank required a different fuel level sending unit, even for the trucks that still had a carburetor.  But, since the gauge system changed significantly in 1987, even those sending units weren't long-lived.

Then there's the valves that were used to determine which tank supplies fuel.  These, too, underwent several changes in this era, from the simple 3-port unit to the 6-port unit in later years.  Further, there were at least two versions of the 6-port, and when they fail there can be some odd symptoms - like the tank you aren't using overflows.

Given that, I'm attempting to provide the necessary documentation to allow you to figure out what you have and how to deal with it.