[Danger4u2]

The J-B Weld worked great. It made a good bond, I think it will hold well. If not I'm no worse off than when I started. The alternative is to cut the spot welds of the flange without cutting into the tank and tig welding the hole. That might involve plastic bead blasting the tank and repainting it.
So on to the rust issue. I made a petcock block off plate to cover the petcock hole, making a gasket from thin rubber. I used gas line for 2 of the 3 smog tubes capping the center one with a vacuum port cap. Then I added 1 gallon of vinegar, two cups of 36 grit aluminum oxide (Alox), topping it off with another gallon of vinegar. Alox is the same material they put on sandpaper and the vinegar is 5% acid to eat the rust. To give the Alox the grinding action it needs I stuffed the tank in a padded cement mixer. I put the tank in, filler neck first and let the mixer run for one hour level with the ground like the tank sets on the bike. I swapped the tank around and let it run another hour. I'm letting it sit over night then I'll run the mixer at a 45 degree angle for a half hour then swap ends for another half hour. The tank doesn't have cancerous rust so I won't need to coat the inside with any epoxy material like Cream tank coating. If all looks well inside I will rinse 3 or 4 times trying to remove all the Alox, then neutralize the acid with Arm and Hammer baking soda and water. Then I will rinse two times with real hot water. That will heat the tank speeding the drying process. Last I will use a compressed air nozzle in the petcock hole and put a shop vac in the filler neck.
That should do it. It's a long process but the cost is no more than $25 dollars and my time. Next....carb cleaning.
Post Script: The cling wrap was used to cover the gas fill hole. I folded a piece 4 layers thick, a little bigger than the gas cap, laying it over the hole and locking the gas cap to keep the vinegar from leaking out of the vent hole. The quarter is sitting in a small amount of the 36 grit Alox.