340 HP's vs headers

I wouldn't waste my money on 340 manifolds. If you don't want headers you could dig up 360 manifolds for free or near it gain a couple hp. 340 manifolds are only a couple of hp over 360 manifolds but cost about the same as headers.

Headers are a good addition to any engine but don't start becoming mandatory until around 350 hp. Especially cause of cam over lap needs free flowing exhaust.