[Tom Goldman]

I've welded bungs at 16"+- on all my primarys and one on each collector close to the merge.
Tuning by the primary readings is the best place to start. ....I've taken readings in all 8 primarys, using just a single channel O2 ,and now just moniter one.
After you have a baseline established ,you could move the sensor to the collector and moniter the readings, but the primary will tell you much more about lower RPM than the collector.