It measures 76.5" at the widest point. Trying to help a friend out here, so it's kind of a 'Pay It Forward' post. Plus, once we ID this he has 4 of them to get rid of. I got in the mix when it was marked '66 Buick Special,' and he knew I needed one.
I believe the corners are different on the '66/'67 Chevelle rear bumper, and the '67 has back up lights in the bumper. (Pic stolen off the 'net)