Couple of sanity questions before I buy/install the oxygen sensors on my exhaust.

I'm running a 96 Explorer EFI set up with shorty SS headers/dual 1-1/4" exhaust.

Is there a "suggested" placement/length for the O2 bungs from the header or will any place work? (I'm thinking about 6-12" from header flange)
When researching the O2 sensors I notices that there is "before" or "after" catalytic convertor O2 sensor, I'm needing the before correct?

I feel like someone told me the distance from the header collector flange should be twice the diameter of your exhaust pipe.

Yes, you need the before Cat sensors.

Thanks Tim!
Just wanted to double check, I've researched anywhere from 6"-8" and you should have at least 18"-24" of pipe after so that way you don't introduce a "backflow" of oxygen which I'm not sure how that's possible?

Also make sure the sensor is mounted between 9 o'clock and 3 o'clock on the pipe. You don't want it on the bottom half to avoid water from damaging the sensor.

rule of thumb for stock O2 sensor is about 12" from collector form my recollection. Most AFR sensors are recommend to be mounted at least 16" from Collector. In both cases they need to be before any cats if installed. As mentioned, the sensors need to be mounted so that condensation doesn't collect on them so in the 9 to 3 o'clock locations.

Thanks for all the info guys! I'm picking up my O2 sensors today on my way home.