Went to Advanced Auto Parts, got the header studs in the size mentioned above, worked like a dream.
I am glad I did this because holy shit, one of the bolts was basically sitting in the hole by force of gravity alone. I think it rattled itself loose and then chewed up the threads. I could slide it in and out as if it was too small for the hole.
I definitely think this is the easiest way to do it. Even helicoiling it you still have to wrestle with the TMIC a bit to line it up. This way, it will slide right onto the studs.