Hi Steve,
I've just done this on an 03 car, and to get the cap to fit properly I had to remove the "internal flange" from the filler neck...the bit that located the metro style filler cap.
Otherwise, when you fit it all together, not only does the pin foul, but you can't get cap in either ☹️
Removed by chain drilling and filing, but if you've got a dremmel or die grinder it would be easier
Oh, BTW the larger cut out in the outer ring goes at the top to give room for the filler nozzle.....