When I dropped my tank a while back it was a rather easy job, of course make sure it's fairly empty like stated above. I started out as just needing to replace the spring, so much for a nice simple job. Mine was clean but had some surface rust that was easily cleaned up using OxySolve from a company called Eastwood here in the states. It was a messy job but well worth it, I then primered and painted it with a silver zinc paint made for gas tanks. Putting the tank back in is a bit of a pain, getting the rubber lines connected while at the same time lifting the tank was not fun.
If I had to do it all over again I would have cleaned the tank up and put a layer of fiberglass over the outside, then painted that. Also one thing to keep in mind is that some tanks have a rubber/plastic bladder inside them, I'm not sure what year that started though. These baldders are known to collapse over the years which results in you being able to put less fuel in the tank, then it's replace the whole tank time. And if you have an 81 like me, there are no replacements made.
One last tip, if you have your tank out pull the sending unit and check it, also replace the filter sock on it. It's a press fit so it will take some effort to get it off.
