74 Dart. Headers vs manifold.

So I have a 74 Dart swinger(318, 4 barrel carb). It’s my daily driver and now for the next year I’ll have to drive it 20 miles to and from school In traffic both ways . Takes about a hour. I currently have **** mileage already and was in an accident and rebuilt the front end and now have to make a decision between manifolds of headers. So I’m just trying to go the route of which will improve my gas mileage. Would appreciate any help