Start here...
https://lateral-g.net/forums/show...=35882&page=10
...and read through my ongoing saga of fitment issues with Dynatech headers. I can show you more reference that they are incorrectly built. They should have been built with another 1/4" clearance at the #5 primary tube. The company claims that 18" from head to head is the correct measurement for the stock motor. My research and own findings prove the actual measurement is 18 1/4" for a stock motor. Motors with aftermarket heads, such as mine, yield even more clearance issues. As of right now, the company has expressed no interest in fixing or even admitting they have a problem with their headers. They also will not allow me to speak with the engineer there again that built the headers originally.