I just mounted my Westach combo gauge yesterday. I drilled and tapped at the same location as Rankram with the exhaust almost plugged and with the engine running. I drilled using a right angle drill attachment with a small pilot bit first and then with the regular size bit at a slow speed. The shavings just came off in a spiral like for RonsRig and blew up the drill bit. Then I shut the engine off and tapped using thread cutting oil. I tapped a turn or two then removed, cleaned, and reoiled tap. In between I also periodically used a pencil magnet, which grabbed enough very fine shavings to barely cover the end of my pinky finger after everything was said and done. The oil grabbed most of the tap residue onto the tap flutes. The drilling and tapping took all of 60 minutes (which included 15 minutes looking for the 2 ferrules that fell of the EGT probe fitting into the engine compartment and then drinking a beer after I found them!), whereas all my research on the TDR in regards to giving me encouragement to do this myself took about 6 hours! Good luck!