these bumpers are made of spring steel.Gotta bend it 4 inches to take out a one inch bend.Put a long straight edge up against it from end to end.A good level will work too.If its bowed you will see it.Good luck.
I dont have any pictures the show the gap and I sold the car years ago. THats why I ask about the gap in the center. As long as the tail light panel is straight, the gap in the center should be the same all the way across it. If it gets wider as it goes out from the center, then the bumper is bowed and would explain the gaps on the ends.. If everything looks straight, I would try another set of mounts. If the bumper is bent, you can send it to someone like Tri City Plating and they will straighten and rechrome the bumper.
My Bad....you were...moving a big bumper back...not straighting a bumper...when you ran into the telephone pole... DFF...:Handshake