Welded the bung (heh heh) onto the exhaust today. Went fairly well, all the prep was done yesterday so it was just a matter of tacking it on the high spots (because collector is round and base of bung is flat), smacking it with a hammer to slightly dent the pipe and make the bung flush, and running the bead around it 90 degrees at a time.
It seems like it sticks out pretty far but I triple checked the directions and for this sensor I guess this is right, just the tip (heh heh) goes into the exhaust stream. As long as my mock-up in the car was right, should be good to go for wideband with adequate floor clearance if this car ever gets put back together.
Not pictured: I threw some header paint over the bare metal, and also ran a thread chaser through the bung which somehow didn’t need it at all, despite being red hot inside after welding.