Ok mabey I can help you. On my 95 gsr and teg fans 97 gsr, we had no problems with the bolts that connect the cat to the heater. The nuts on ours were not welded on, so just make sure we are talking about the same nuts and bolts. Your talking about the ones with the springs compressed between it right??.

now for the o2 sensor(you have obd2) is at the back of the cat. what you have to do it pop the rubber tab up where the headshields are located, and I believe you can just pop if off from there. I hope that works, please feel free to ask away with Q's