I chucked the smooth shank of the broadhead adapter in a small drill press and held my mill,broadhead file against the side of it.
I kept one of the inserts handy and when I got close,I stopped the press and tried the insert for fit.After that,it is just one or two file strokes and check again.It only takes a couple minutes.
You also have to make sure the insert flange isn't wider than the shaft.
For this,I used a cutoff piece of shaft,put the insert in it and chucked the shaft piece in the drill press.Just a couple strokes with the file and the flange is flush.