I agree with
miljnor, why not make it 'better than the original'. Take a look at rotary broaches for a wide variety of standard hole shapes. For $50-100 you can get a stock broach with a hex, square, serration, etc. and wobble it through. If you don't have a broach holder, some guys try to push the broaches through in steps as a test.
www.slatertools.com