Its hard to drill deeper than the hole. If unsure, I would literally grind half the point off the drill bit, leaving the end flat. It will then only drill to the bottom of the hole. To break the tang off, you use pointed pliers. So you dont need a hammer... Or insert it upside down so its on top and easy to see. And you would coat the threaded insert LIGHTLY with red loctite. You dont want it getting into the new thread.
Are you sure about Helicoils working upside down? As you know I had to Helicoil all of my first set of primatic cells, and I tried this technique. It didn't work for me, I realised that by turning them upside down as you turn the coil spring clockwise it actualy makes the coil expand rather than contract as it does when you use it the right way up, so as the coil enters the tapped hole the friction builds up between the coil and the tapped hole too much far before the coil is seated correctly and then the tang breaks off too soon. Well it did for me anyway