Take the guard off, back in the vice(padded with leather) and break out the hacksaw.
And files. It goes much faster if you file the one side to your line (see pic below) and then the other side to match......and finally bring the center down to meet the bevels.
Another filing tip. A file is meant to cut on the push stroke, and a lot of guys will tell you to only file that way. That's good advice, but if you lift the file at the end of each stroke it will clog up and all the grit in the teeth will scratch deep grooves in the piece you are working on.
Instead reduce the pressure, but keep the file in contact with the work and pull it back towards you for the next cut. This keeps the teeth much cleaner and you'll get a lot more cutting done than if you have to stop and clean the teeth with a brush every three strokes. And you'll have a lot fewer nasty gouges to try and smooth out later.
Filed to the lines in profile.......drift it back on and check for center and balance.
Looking a bit better.
This one is going to be s shaped a bit, so after making adjustments to the profile to get it lined up just right, I take it off again and put it back in the vice. Padded on the inside of the curve with a hardwood or brass block......outside with leather. I do this shaping cold. If I needed to make a more drastic curve, I'd probably just forge the thing to shape instead of doing all that filing. It takes a fair bit of force to curve the guard, I am using a 12 inch crescent wrench for leverage......note the copper shim(penny) on the underside of the wrench jaw. This keeps the sharp jaw from biting an unsightly deep notch in the guard.