I recieved my sights yesterday. I ended up ordering a 7.5, 8.5 and 9.5mm bead, and a 10mm blade. I had time last night to fit the 10mm blade - it required some minor filing off the bottom of the sight (as Rule303 mentioned above) and a small amount out of the front recess for the sight base retaining pluger in the sight base. I thought I'd do the 10mm first since it is larger and easier to hold when I filed it (I don't have a vice).

The 9.5mm bead will likely do the job for the 270gn projy's that I want to use. It should make the POI slightly low which I can the compensate for with the NECG rear sight adjustment. Alternatively there would be enough adjustment in the NECG to use the 10mm blade - I'll try both and see which one I prefer. I suspect that it may be the blade.