This is a pretty straightforward job but is potentially dangerous due to the fuel. Think through how you will drain your existing tank if needed and have containers ready.
Start fresh with a new fill hose, sending unit and lines. If you get the plastic tank make sure you order one of the thicker circular tank / sending unit gaskets. Once you get everything installed, don’t go fill her up. Pour in a bit of gas slowly, go underneath and make sure there is no leaking from the fill hose or entry into the tank. If all is good then pour in a gallon or two. Make sure no leaks in the sending unit area, check very closely. If no leaks, start it up outside and let it run for a few minutes. Shut it off and check again. If you need to adjust the seal don’t hammer on the ring, you don’t want to make a spark down there. Keep adding fuel slowly and checking.