I procrastinated long enough, but tonight I finally got around to treating the gas tank for the rust inside.
I poured 2 quart bottles of LimeAway into the tank, swished it around and set it in different positions for 30 minutes at a time to let that sh*t do the job.
This went on for 7 or 8 hours and there is still a little surface rust appearance (but no loose corrosion or flakes). I even sat it upside down and let the stuff eat away the rust away where the cap goes in. Saved me using naval jelly.
Then I ran the water hose through it for close to an hour at a slow rate. I shook out the water and added some gasoline. Hopefully it won't flash rust if I keep it swished around.