[Jeff Lee]

Eric Bell, who has a "reasonably fast" 440-6 SS/E & FA Challenger, went from the header builder I have always used to Performance Welding. As I recall, in back-to-back dyno testing the PW headers were worth 15+ HP.
His style in building headers (from what I have seen) is exactly what I think is a prerequisite over "tuned length" headers, that is, Mark wants long stubs off the exhaust port and "swoopy" curves more so than being +/- 1/4".