Heli-coil questions

The box the heli-coils came in, said to use a 29/64" pilot drill bit.. and the 7/16-14 tap for the install.. I already did it, was just wondering about how the allen head fitting/plug whatever would work if i drilled the center out and tapped it for 5/16".. The heli-coil is already installed, just dont want to pull the head and redo something if it fails. One more question, do you pull the little tang, in the heli-coil after install or leave it there? Yea, my dad has some bada$$ drill bits. I "borrowed" one, and drilled through the broken tap. But the hole was enlarged, and piece of the head cracked (inside the hole) which is the cause for the big ol' hole lol. thanks for all the input guys, it jus scares me a little since it leads into the water jacket.