Glen when you do yours do you completly remove the part of the flange that locates into the cylinder? I went as thin as I dared on that lip and its still not big enough, I think if I ground the lip completely off I could smooth in the rest but then wouldnt exhaust sealing and blowing gaskets become an issue?
I ate through 2 grinding tips and ruined my burr tip...... Im also semi deaf as the compressor ran constantly trying to keep up with the die grinder
Before....

The port is about the same size as the gasket!!!

2 of the bits I used..


And after...


You can see how the top part is still off a little...


