Greetings from NC!
I have been building headers for professional race cars for over 16 years. I am new to this forum and forums in general. I wanted to jump in on this thread to confirm what a lot of people are learning and that is that a 421 header is a better headers design for any application, street or race. They can be a bit trickier to size correctly and if too large do not show the increases that are possible. I am a high end builder but am happy to offer my opinion as there are a lot of people confused about what is important and where to spend money!
Thanks!