Luckily, i didn't end up having to drill.
here's what I did.
1. screwed the bottom portion of that threaded insert into a nut, which I could then hold in place using a wrench; this gave me much better grip on the whole threaded insert and allowed me to twist the bolt back and forth as I did below.
2. sprayed WD40 onto the exposed portion of the bolt, and then re-tightened the bolt into the thread insert so as to lubricate the inside of the threaded insert.
3. loosened the bolt until it reached the point where it became stuck again in the threaded insert, and added more WD40 to the exposed portion of the bolt, and then re-tightened.
4. after 2-3x of doing this, I was able to completely unscrew the bolt from the threaded insert.
5. I then needed to use pliers to unscrew the threaded insert from the nut I had used in step 1, which was no easy task
6. I filed down end of the bolt that was giving me trouble, getting stuck in the threaded insert
7. applied anti-seize to the bolt threads
8. Used JB Weld on the outside of the threaded insert and re-inserted it into the intake manifold
9. Now I'm letting it cure for 24 hrs and then I will screw the ignition coil back down using the bolt that I had filed down in step 6.
What a pain.
2015 High Roof Extended Length