New rear bumper not fitting 71 Mach1

[JJHstang]

Replaced the rear bumper on my 71 Mach 1. Used the old brackets and bolts. As you can see from the attached pictures the left side is a lot lower or gapped.
I can't see any way to adjust the left side up. All bolt holes are round not slotted or have play to make any adjustments.
I don't recall the old bumper being misfit.
Looking for thoughts on what I can do or what I don't know.

 

[JJHstang]

Just to let everyone know I did get my bumper on correctly. I found that there was enough play in the horizontal slitted bolt holes that if I lifted up on the left side while tightening the bolts and pushed down on the left there was enough play to level off the bumper. I did flattened out the washers on the right side and tried to hammer the right bracket a little straighter.
Live and learn, trial and error.

 

[2Blue2]

She's looking good now
What a neat car!