Looking at a set that has the flat flange on the 4in side. I assume it is a mercury header ? Can I have tails made to fit these since there not the rope seal? We're these made different than the regular cmi e tops internally ? Thanks

CMI can make you tails... or you can buy the flat flanges & clamps from them, and have anyone make you tails. To answer your question... yes the flat flange was used by Merc