Depends on how much money you want to spend. A new tank would be ideal but the old one can be used.
I'm assuming a '46 tank is similar to later models with the tank behind the seat. Are you sure the tank has a baffle or are you just hearing something loose in the tank?
The sending unit is pretty fragile; a float runs up a spiral flat strip. That can break off and rattle around. A new sending unit is not expensive and easy to install.
As for the crud and light rust I would pour phosphoric acid in it while the sending unit is out, let it set overnight, flush it out with a garden hose or use a pressure washer if available. If there is still visible rust or crud just repeat the process until it is clean.
The acid will leave a coating that will resist rust for a couple of years. If no water gets in then the gasoline will keep it from rusting.
