With standard bore I think it should be 6 to 8 thou clearance.If your gap is less sounds like you have oversize rings
A fine file will do but only one 1 piece oil ring kits as I recall.Today the oil ring is 3 piece would not recommend filing down as the clearances differ to 1 piece.
Hope that makes sense to you.Bryanj may update me on that?
Cheers
Bitsa