Toby,
First off, I am by no means an expert on the Bradley IFV. This image shows what I think is the end of the above mentioned bracket on the Right Side Armor:
This image (original from Prime Portal) shows that the bracket is not present in the vicinity of the exhaust and the cooling (?) screen:
I believe the hex nuts are for either clearance of the screen assembly or for mounting this bracket - angled piece below the exhaust (image from Prime Portal):
I've noticed that from the outside of the plates, there are smaller hex bolts that seem to correspond to the brackets, and larger hex bolts correspond to the hex nuts (original image from Prime Portal), Note that the above bracket is not present in this image:
This image shows the bracket I believe is held in place with the hex nuts:
The left side appears to have a continuous line of smaller hex bolts on the outside of the armor plates (original image from Prime Portal):
Does all this make sense and hopefully give you an answer? If someone actually knows the answers, please correct me...