Dougs VS TTI Header Flanges
It looks like the Dougs flange would better match the ports then the TTIs. If that is the case then that is a serious advantage the Dougs have; better flow and better sealing.
I called TTI and they said the header has to come off and the header flange bead needs to be widened so that it will contact the outside of the heads exhaust port. I have a guy locally that specializes in custom headers who will be doing the work.