Where to add2nd o2 bung for wide band o2

[hybrid89]

92 hatch GSR w/ Rev hard stg 2 kit. My buddy needs to add a bung and a plug to his down pipe so when the dyno it, they can screw in a wide band o2. where is the best location for the bung?

matt

 

[phunky.buddha]

End of downpipe, right before the cat.