When you get both of your O2 Sensors in the mail it will not matter which one is plugged into either the front or back. Primary O2 Sensor will plug in somewhere near the back of the motor near the general location of the oil filter... The Secondary O2 Senser usually will be under the car near the catalytic converter's general location... usually pops out of the under carage of the car just before the shift stick.

There's always an option to just running a OBD1 chipped ECU like a P72 or P28 and converting from OBD2 to OBD1... less worries to deal with concerning O2 CEL's..