I had mine welded in on the head pipe side going towards the rear of the car right at the collector flange with a full length 3.0 inch exhaust system with straight through muffs mounted at the rear bumper behind the rear end up
I ended up making it a dual wide ban system later so I could read both sides at the same time before adding the hardware and software to read both sides I would swap the O2 sensor from side to side realcrazy
My message is do it once and do it correct with both sides working from the start up

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)