I'd use a flat file to take off as little material from the inside rear of both dropouts until the axle just goes in. This way there'll be no alignment problems. Chrome poses no problem, a sharp file will go through in one pass. I'd use a round file to finish the curve nicely.
Although.. If you file the axle you can swap front wheels back to a smaller axle with no problems.
I'd use a flat file to take off as little material from the inside rear of both dropouts until the axle just goes in. This way there'll be no alignment problems. Chrome poses no problem, a sharp file will go through in one pass. I'd use a round file to finish the curve nicely.
Although.. If you file the axle you can swap front wheels back to a smaller axle with no problems.