Headers for my 71 Demon 340.

[ir3333]

If you have a stockish cam and a large 275 (28") rear tire a 3.55 gear might be a more noticeable gain at lower rpm if it's just driven on the street.Some don't like the higher rpm of 3.55 gears with small tires .
There are guys on here with performance experience that could tell you what would be best.
Most guys like the appeal and performance of headers though.

 

[Unconventional]

Most guys like the appeal and performance of headers though

A good set of tubes and turbo mufflers make even a 2 bbl teen sound good