I get a side bar link to a Partgeek ad that lists 75-76 as a different part number then 77-80. Yet, the external dimensions are listed as the same. I know at some point Ford went to a longer filler neck (to keep it from popping out). I'm assuming any difference probably has to do with ventilation and vapor recovery. However, they might have made tank design changes for their "problem," or such changes as spare tire well size change (space saver spare), different fuel senders etc..
Measure your tanks dimensions, see if they match the tank you have and perhaps it will work just putting caps on certain hose connectors of later cars. The more critical aspects would be the filler neck and fuel sender. Search and see if they have similar part numbers. Anyone have a Hollander Interchange book?