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.

We cannot solve our problems today using the same thinking we used when we created them!

Albert Einstein