Pretty much any decent exhaust shop can do this job for you. Just drill a hole where you want them, and take them to the shop. Most shops have the bungs, too. I placed mine in the #2 and #6 primary pipes, about 3" up from the square flange.
I had mine placed at the bottom of the tube, where it wouldn't show. However, it was later suggested to me that it should not be placed in the very bottom of the pipe. Any condensation, oil, fuel, whatever, that runs down the pipe could contaminate and destroy the sensor. Oh, well. Live and learn.