Thanks for the info, guys. Actually, a couple years ago, I was doing a clean-up on the underside, and dropped the tank just to clean it up. Everything looked good then, and since there wasn't much gas in the tank at that point, I threw out the old gas and put new gas in there. Also, even though we don't drive the car, throughout all the years we have started it up and run the engine at least once a month. That's used up gas that we replenished with the gas can every now and then, so what was in the tank wasn't gas all the way back from 1974, it's just that we've never had it as full until a few weeks ago. We just submitted for historical plates, which is why we were trying to fill up the tank.
It doesn't look to me that there's a problem with the connection at the fill tube. I might be wrong, but looks like there may be a very tiny hole about 2 inches to the left of the fill tube, and I would rather not drop the tank if it can be fixed by some kind of epoxy or something. It's easy to get to, so at this point all I want to do is plug it up, if there's something good to do that. If that doesn't work, then guess I'll have to drop the tank, drain the gas, fill the tank with water and flush/dry, then solder it closed. Just wanted to avoid that if possible. Thanks again, Mike