I certainly hope that you've used a Klann or SirTools style spring compressor and removed the rear suspension springs before getting to where you are now.
If you have not removed the springs, stop immediately!!! Removing the trailing arm pivot bolts without first removing the rear springs has the potential for causing serious personal injury.
When did the bushings on Thing One's car, we pulled the springs, pulled the shocks (his is a TD) disconnected the emergency brake cables and then dropped the front of the subframe. The trailing arm bolts weren't easy to get to or get loose but, we were able to do it.
You might check out dmorrison's thread about rebuilding the suspension on his W123:
http://www.peachparts.com/shopforum/showthread.php?threadid=60964&highlight=bushing