1970 Swinger 340 sending unit

If you can get a restored OEM fuel sender that is probably the best option. That would be the easiest. If you use an aftermarket, you will need a Meter Match it get it to work decent.

Mine had an aftermarket sender in it when I bought it, so I just learned how to deal with it.

There are a good gas gauge threads on the site here that explain a lot of it.