Again, I don't know why they put that warning there. BTW, there were several different versions of Fenton headers. I had the originals. Maybe later versions didn't work with the Offy manifold. Mine worked with no problems, but I got my Offy and Fentons from a 1955 235 that had them mounted when I bought it, so they were both from "back in the day". Maybe latter versions didn't work with them both installed. Mine worked with no issues.
