HighC,
If you put it in like this you won't need to paint or tar it...
http://www.yachtsurvey.com/fueltank.htm
If it's still good, you gotta think, it's been in there 30 years with no pain or coating and it's still fine...it will likely be fine another 30 years from now sans paint.
Make sure you take the strips off the bottom of the tank (if they are still on there) that's often where the worst corrosion is.