Welcome to Dr. Björn's Auto!
Vanagon Fuel Tank (2wd, not Syncro, not Diesel) for 86 and later model style with 50 mm fuel filler grommet. If you have a 80-85 model or you may have the larger filler pipe. You can replace that with the smaller diameter filler pipe.
Recommendation: change filler grommet and vent lines with respective grommets as well. An o-ring for the fuel level sender is included.