correct me if im wrong........obd1 has 1 O2 sensor and obd2 has 2 O2 sensors? and isnt there always one on the header either way? i have a 95 gsr and the motor was swapped and when i did the exhaust there was a o2 sensor on the cat as well?

 

yes that is correct

obd1=1 o2 sensor
0bd2=2 o2 sensors

for an obd1 GSR there is an o2 sensor before the screens of the cat, and for the obd2 there is an o2 sensor before the screens of the cat and after the screens of the cat