Vacuuming out the fuel was a relatively desperate act and will not be repeated.
Thanks for the concern. I like speaking with mot of you guys and the few of you I've met or talked to outside of the brickboard have turned out to be really decent folks. Rest assured, I won't be firebombing myself anytime soon...

Anyway, I drained the last of the fuel out the drain hole and removed the whole tank. I power-flushed it with a hose and let it dry out overnight. I sealed up the cracked weld with Black POR15(tube form) and gave all the exposed metal a coat with rustoleum primer. I then dropped the tank in, with a new layer of rubber/clay putty along the edge. I then poured a half gallon of clean gas into the tank and let it drain out into a catch pan. I strained that out and repeated the gas flush a couple times.

I rebuilt the fuel level sender and bench tested it (10 - 200 ohm seems to be the range. after re-installation and reconnecting the battery, It's reading around 1/2 - 3/4 tank after adding 6.5 gallons to the tank. That sender was completely encrusted with rusty deposits and I used my wire-wheel to clean it up. After re-attaching the sending wire I coated the nut and connection with dielectric grease to prevent future corrosion.

As far as the filler tube, I looked for it inside and could not see it, so I removed the fittings and ran an 8 gauge wire through. I felt pipe-like resistance pretty far into the hole, so I guess it's mostly there. I guess I'll just have to see what happens. Maybe I should put a spare gallon of fuel in the trunk... Although that's unsafe in its own right.

After reconnecting everything, it runs well and the fuel level reads good. I also took the opportunity to install new limiting straps, but I found a hole in my exhaust, so my list of things to do has not shrunk.

If the problem returns, I'll see about removing the fitting and sodering in a new tube. I've done a little sodering (such as when I pulled and repaired my 940 sending unit (see the BB FAQ for that), but I've never done large metal. I need to fix the top brackets on my 1800-style radiator so I need the practice.

Thanks for the advice and help.