You might want to search for "aftermarket sending unit" on this forum and do some reading. The short version is all aftermarket sending units are linear. Your gauge won't read correctly. In order for it to work correctly you'll need to add something like the "Meter Match" device (search for that as well).
I've seen old sending units that weren't that bad. 2 common cases of a fuel gauge not working is lack of a grounding strap at the sending unit, or the brass float has a hole and is full of gas. You can replace the brass float with a plastic one:
https://www.amazon.com/dp/B003AOM17I/?tag=2402507-20
You can also buy strainers new:
https://www.amazon.com/dp/B000ES5N5U/?tag=2402507-20
Another option is to send the sending unit in for repair/refurbishment. Several places offer this service. They might even have one on the shelf they can swap-out with you:
Fuel tank sending unit rebuild service
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Rebuilt Fuel Sending Unit Specialist
