400WHPITR

I recently bought and 2000 itr with (b18a) ls/vtec turbo. The car came with a p73 ecu (OBD2 ECU) with an obd1 wiring harness conversion. To make the story short, the MIL light came on and I manage to retrieve dtc code 1 which is the primary o2 sensor. Since the wiring harness is obd1, there was only one 02 sensor being used, located on the downpipe. I was just wondering if anyone can give me advice on which year and model should I look for when ordering the o2 sensor? Any help guys, I try to search but could find that much help on the topic.