A 1/2’ bow is not a lot. Straightening it would generally require an over correction which could damage the plating. A few years back, I straightened a 28-29 bumper bar in my shop press and the required over correction damaged the brittle plating; but I got it back to flat. It then would have needed replating.
Since it is only a 1/2” bow, you might try using an oval center clamp, and mount your license plate there. Use a full height backing plate. It just might pull the bars back to the same bow.
Since it is only a 1/2” bow, you might try using an oval center clamp, and mount your license plate there. Use a full height backing plate. It just might pull the bars back to the same bow.