I've been there, done that.

Use a sawzall.

The issue is that the bolt is siezed in the bushing, but not for the reason you might think.  It's not that the bolt has rusted or corroded into the bushing (since they are different metals), it's because the bushing is no longer straight.  Over the years, or from overloading, the bushing is bent and that's why it's siezed.

If it doesn't come out by driving it out, then use the sawzall and, like someone else said, stay on the rubber side of things.

This is important to know for installing the replacement trailing arms.  You might plan on putting in new bushings.  If the replacements are also bent, you'll have a hard time getting a bolt through.

Kim Springer