Shorty Headers
i say if you can get the step headers to fit to your liking use them. picking up some precious torque in the midrange and getting some horsepower when you're legging it out instead of shifting on the course might be worth fractions of a second.
i wouldn't say that headers would be "necessary" for your application and intended power goals, but i would certainly recommend it, or 340 manifolds if you've got those on the shelf.
will shorties be better than manifolds, sure but not by a wide margin. it's up to you to decide if that margin is worth 7~800 bucks.