63-66 A-body header alternatives
I have the Spitfires on my 360 Valiant right now. They're better than cast iron manifolds, but not by too much. I'm running mid-12's thru them, but am ready to step up to the Dougs D-450's as the Spitfires are holding me back. Bigtime!
If you're running a street car, the Spitfires will be fine. If you're looking for high end performance, spend the money on Dougs. I've seen mid-10 second cars running the Dougs headers.