Cheap *** headers at it again!!
Putting dents in headers does affect the performance of the headder. I personally don't have a car with headers on it but a real good friend of mine has a 1974 dart sport 360 4 speed with p/s and his headers fit like a glove. He has Doug's headers, pricey yes, but the fit is awesome. I asked him about putting dents in headers and he said that if you have to do that that you're better off staying with the manifolds. He believes that you get what you pay for.