@toolheadSo, you throw away the h washer
You open up the two holes in the finlike projections that fit through the h washer
My understanding is you are opening up the hole enough for clearance of the ash can retaining bar thing (so you don't have to bend it down towards the kettle, like one of another solution).
I assume you use the new sweep handle, not the old one or is it vice versa?
I've picked up files dirt cheap at garage sales over time. I should have something that will work.