Question on headman headers

Don, I have them on my Dart. I used 2" hole saw and made a short slot for the tube to go through. I spoke to Ryan Johnson about these or the TTI's and was told the Hedmans make more power. I don't remember the number but it was surprising.

I dont want to have to cut anything. Was hoping they fit like a TTI, totally underchassis.
I used to have W5 Tti's they fit good, but also heard the Headmans make more power.
May have to rethink this