better not be and you can't run evacs in frt of the o2 sensor i put my bungs @4-5inches past the collector points.
If you are just measuring a cylinder bank the above mentioned is a good location. If you want to measure individual cylinders about 10"-12" from the port is about the best. This gives a good consistant reading without messing with the signal at the carb.
What about the clamp on style? Innovations makes one that can be clamped on th ethe end of the exhaust. This way you dont have to weld a bung
From what I have read the clamp in style, is used mainly
on a dyno. and its not very accurate, you will want to
weld a bung into your headers, if you are wanting to tune
your engine rather than read each cylinder you will have to
locate it in the collector,just after the tubes merge.
make sure you purchase the wide band, I have tuned a carb
engine with a narrow band, but you will find that at the most
power will show rich on a narrow band.