Hi,
Don't mess with them since the interior ring cannot be removed unless the tank is cut open the ring cleaned up or replaced then the tank is re welded then install the new parts.
If rusted the neck filler is screwed into the interior ring and is usually pinged in the treads so even if you try to unscrew the filler you will rip up the tank.
You can cut the filler neck in to 3 places trying not to damaging the threads and take them out in pieces but risky business..
New fillers can be had as mentioned. Gaskets from Mcfarlane can be had.
Best you can do is send it to hartwig fuel cell repair. Spoke to them a few times and they are the only ones I know that can bring them back to life...
Link:
https://www.hartwigfuelcell.com/repairmetal.php The wings have parts in them for the conversion of standard wings to LR wings that are needed to convert standard wings.
If you use the original parts in the wings you just need a 337 describing the conversion referencing parts manual and get them signed off (NO STC).
Installation would be another 337 to install to be safe..
Don't try to remove the rusted parts yourself. you will not be happy with the results and most likely destroy very rare tanks..
SAVE the Wing parts... also impossible to find.