Well here is a nice little apprentice project for you. The "lump" is most likely deformation from the rivetting process used to attach the blade to the stock, right there where the lump is.
A few careful licks with a 10" millsaw file should bring it back in line with the main stock.
You might want to grind the teeth off the edge of the file that will rub against the blade so it does not scar it up. Proceed slowly with care, taking long, gentle strokes (ooh er mister). Check it against a known good straight edge until no light is visiible between the stock and the straight edge.