To remove the filler neck, you need a spanner wrench. My KR Wilson catalog from 1940 doesn't show they made such a wrench but that isn't a definitive statement - someone more familiar with KR Wilson or other tool manufacturers may know.
If you search for spanner wrenches, there are 2 general types. A pin spanner and a hook spanner. The pin spanner has a cylindrical pin that is supposed to engage a hole in whatever you're wrenching. The hook type looks essentially the same but uses a flat face to engage a the nut. I believe this is the kind you need. Several manufacturers make wrenches. Here's a link to the Snap-on option which is adjustable for 1 1/4 inch to 3 inch applications and shows a picture:
https://store.snapon.com/Adjustable-...h-P633838.aspx
The fuel tank neck is approximately 2 1/4 inches.
I don't have a spanner and you can see from my post that I can't access the nut with such a wrench. I might be able to loosen the tank and extend it out the driver's side, remove the filler neck, then pull it through.
Last thing - don't forget the new lead washer when you reconnect your filler neck. The lead washer is designed to deform and create a seal. Reusing the old one or forgetting to install one will likely cause a leak.