Exhaust Cross Pipe with O2 Sensor

[coop34]

Hey guys. Is an exhaust cross pipe necessary in order for the O2 sensor to operate correctly? The mechanic told me that my truck is running rough because the O2 sensor needs to be able to read both sides, so he said that I need to put in a cross pipe and place the O2 sensor in the middle. My O2 sensor is currently on the passenger side just below the flange.

My truck is a 70 with a 5.7 L engine from a 90 chevy silverado.

Thanks for the help!