Where do you put Oxygen Sensors on headers with collector mufflers

i would say toward the end of the collectors at the 10 & 2 positions.

Try to keep them away from the open air of
the collector.. also keep them upstream of
any input air like a evac.. make sure they
point a little downward so if they get any
condensation on them they will drain off..
what I do is put them in near the front of
the collector but have some space so the gasses
mix before it hits the O2(your after the averages
of that bank otherwise you would put one for each
cyl)

I have dynomax collector mufflers on it. Not a lot of room. Would it work in the muffler body itself. Also, need to no a good controler for this to.

If you run mufflers then you can put it just
before the mufflers.. just make sure its
sealed so you dont suck in air

I have mine in the header tube , in the collector , you have to make sure there are no leaks or you will not get accurate readings.

Do you have a racepak sportsman ?