Don't know if you've started the tear down already but I recommended TimeSerts vs. helicoils as a perfect fix.
My buddy has a $450 kit just for the Ford Headbolts with a drill guide, taps, reamers and inserts.
I bet he would rent it out to you for a small fee and deposit and the inserts are cheap, he even has a few left.
He has built his motor up to redline at 6500-7000 and using stud girdle, H beam rods, FMIC, and anything else you can imagine to his block, then he figured out his head bolt holes were the same way as you describe.
His motor should put out around 370-400 hp and I have full confidence in the TimeSerts to perform as good as or better than a fresh hole.
Just another last minute recommendation before you do the new block.
Good luck