[HO455]

Here are the three under the wood supports. (Photos #1 & #2) Actually the front one isn't really a support but it has the cage nuts for the rear seat and its seat belts. I am guessing that a Burban that came with the third row seat would have a different version of this and possibly one for the third seat too. The seats have been in and out of the WMB so many times over the years all threads in the cage nuts are stripped.
The two 2 bolt hole plates in the back support are where the upper part of the body mount bushings contact.
I failed to get pictures but I was able to get the bolts out of the rear top plate without damaging it. I had to heat them with my Map gas torch and then grab the bolt with a pair if Vice Grips. While wiggling the bolt with a the pliers I tapped the end with a ball pein hammer.