couple of suggestions:
You only need to grind the "inside" of the slot (the side that faces toward the center of the car) on both the front and back end of the toe bolt mounts. (four grinding areas total).
A dremel flex shaft makes getting up in there MUCH easier.
The Dremel #115 cutting bit is the easiest to do this with, IMO, but it's very similar to the #117 pictured above. It tears right through like butter. Pretty cheap, also.
Great DIY. Thanks for uploading it!