Thanks - was hoping there would be some minimal tweaking that could be performed...
The tank was replaced at the dealer shop, but is not a difficult job if you don't mind breathing diesel fumes.
On the 1981, the vertical trunk liner under the rear shelf has to be removed, and then a protective sheetmetal wall covers the fuel tank. Several screws, along top and bottom, hold the protective sheetmetal wall in place. I had to remove the liners for the side wells first - makes it easier to remove the vertical liner.
(The these three liners are formed rigid and are sturdier then the cardboard jobs you see in cheaper cars but a headache to clean soaked diesel fuel since you can't blast through the fabric.)
The filler neck seems to be part of the tank and positions in the filler door opening. A rubber piece surrounds the neck - I guess to keep it from knocking around on rough rides.
Not sure about procedure on fuel line and sending unit. I guess the first thing to do is disconnect the battery before any work is done to the fuel tank.