Hey Curt, the port roof does present some challenges for sure. Its also slanted as well as being thin. I usually just tap it deep enough so the plug can get a few threads of engagement and you don't have to get it too tight to seal up either. Then I mark each plug and dedicate them to their respective locations, tighten them up and blend them to the roof contour with a grinder. That way when you tighten them for real, they don't protrude awkwardly into the port and upset the airflow too much. Sounds like a cool project, but yours always are. Look forward to see how it turns out.
