New rear bumper not fitting 71 Mach1

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.

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.