You forgot to mention that the engine is only rated at 300 HP to start with so I don't think this motor is powerful enough to really exploit the benefits of any kind of header or 340 manifold.
Even with tube headers they only got 322 hp,(and the headers didn't fit properly) and with Hooker headers 319 hp, then with TTI headers they got 327 hp. Finally with Super Competition racing headers they only got 319 hp. I mean, except for the 340 manifolds, all the headers require cutting up your car, so unless you want to cut up your car (not for me thanks) the 340's are not a bad choice. But I can see what you're saying, you might as well stick with the 318 manifolds, if you're using their 300 hp motor. What if you've got a more powerful motor like a 400 hp motor?
How much better are the 318 manifolds vs. let's say my old '65 273 manifolds?
