I have a set of fine needle files, but not very round, may get away with the E string slot but the rest are a lot finer than the files I have. So setting up the nut for height would require a set of feeler guages layed over the first fret ??? Then draw a line across the nut then sand down the nut till the height is matched before filing the slots ??? Ive looked at a few posts that seems to be the way to go ??? Ive also seen where blow torch cleaners have been used as slots files and are very cheap.