We decided to add an Auto Meter wideband O2 gauge to see what was really going on with the engine. The Catco kit has a provision for an after-cat O2 sensor, but the instructions for the gauge state that it should be as close as possible to the header collector for most accurate measurements. While we don’t have headers on the truck, we got the idea and drilled a hole about six inches from the driver-side collector. We then welded the bung included with the wideband gauge into the tube with our trusty Lincoln Electric MIG welder. The gauge instructions suggest using a TIG machine, but we’ve had no problem putting the bungs in with MIG over the years.