The front O2 location is another story. Terrible location and almost always ends up so close to the floor that the sensor won't even go in without beating a dent in the floor of the car. I recommend just plugging that bung and having a new bung welded in at a better location. The top of the crossover pipe is nice, and then you don't even need an O2 extension at all.
Can you really put the o2 there? I just changed mine on my headers and it was a ***** i thought i needed a new o2 bung but finally got it after tapping it with a spark plug tap