Heli-coil questions

Oh the heli-coil is now going to need a bolt with 3/8" threads, i think? Its not going to be the 5/16"ths size anymore.. I was also reading and someone here mentioned threading in a plug, like the ones with the allen head in it. Threading it in, then drilling the middle of the fitting out and tapping it to 5/16th's threads, so that it could use the same size bolts like before. Would the fitting like that work, or would that be half-a$$ed?? It seems smart to me to drill and thread a fitting like that, then you can use the 5/16" bolt again.. Sorry for the rants, just looking for input. Thanks