Maximum power with Schumacher Headers

i got the schumacher headers on my 70 duster with 440 ran power steering for the first year but switched to manual...fit awesome, like them alot as far as power there good on the street sound awesome uncapped... but now im gonna cut the innerfenders and try to track down a used set of fenderwell headers.... but guys i remember reading an article myself on the schumacher headers in a 383 barracuda i think at a test track day and they ran decent numbers