340 HP's vs headers

I traded a 8 3/4 3.55 center for a set of 340 manifolds (68-70) . Steve(4spdragtop) aced them up with a blasting and POR15 treatment. They look mint. I plan to run them on my 318 with the exhaust system from TTI on my 71 swinger until i get a real motor for the car . The rear end was a 741 so I think I did ok (even trade). Ive had headers on lots of street cars. If these mannis work as good as I am told it's a good trade off for the leaks and the hassles that come with cheap headers.........I must be getting old:D