Standard Mk2a knob is 19mm in diameter. I assume that the Mk2 is the same. Surrounding plastic is 24mm.
Standard and Darkstorm cutouts are 11.5mm in diameter.



If I understood Michael's measurements and how they relate to the photo above, then increasing the cutout diameter to 18mm would leave 1.5mm hidden material all around when used with a 303 face or 3mm all around with the original face. That should be enough for concentric tolerance. I suppose you could go to 17mm instead which gives 2mm and 3.5mm respectively.

Improvement in unobstructed knob area would be 168% for the standard knob/face (18mm) or 139% (17mm). 303 face gains a 112% improvement regardless of new cutout diameter as it is limited to a 16mm aperture anyway.