[MFE III]

I welded an O2 bung at about a 45 deg angle down on the inside of the collector. I only did one and haven't had a chance to use it yet. Had my eye on some A/F mixture reading gauges in Summit, but haven't gotten that yet. It's particularly helpful if you wanna dyno your car.
You can pick up the weld on bungs with a plug at Summit, Jegs, etc.