You want to file the leading edges of both the impeller and the bowl.
Think airplane wing, not knife edge (weaker) while you're there, check the radial tolerances of the impeller to wear ring. It should be at ~0.0125" per side (radial), and .025" to .030" at the leading edge, if I remember right (shouldered). Shims will help you with your leading edge dimensions. Wear rings are available undersized based on your skirt dimensions.
Any questions, pm me.
Dan'l