First of all, welcome to iboats. We always like new members...
If you can, post a picture or three of the tank you are wanting to rebuild. You will get a lot more ideas and good suggestions. Sounds like the tank is a typical OMC/Johnson/Evinrude tank. But I am only guessing... Pop up those pictures for better answers. If it is one of those tanks, you can still buy parts for them. Search for such tanks and even visit Ebay for parts. They made tons of them and therefore parts are still around.