What A/F Gauge do you run

Thanks mad dart.
I'm running stock manifolds on my 360. Would it be safe to weld it right where the downpipes come down and start to go horizontal along the bottom of the car (so around the front of the transmission)?

Since I'm only installing one bung, is one side of the exhaust better (passenger vs. driver side) then the other. I'm running a H pipe dual exhaust 2.25 inch