Got them apart!

I was able to take apart the rear bumpers. The bolts holding the sections together had gotten fused in place from rust, and tons of pressure from my press would not budge them. I heated each bolt with a blowtorch for about half an hour, and then plunged them into water. After this shock treatment, I was able to press out the bolts (along with piles of rust).

I also used my press to straighten a couple of the bumper brackets that were slightly bent.

My next project: replacing a couple of broken-off studs on the front seat tracks.