Thanks for the detailed replies.

Unfortunately I no longer have the Timesert kit to experiment with but I did put a camera in the hole last PM. A little hard to see but no debris is evident. I put one of the old head bolts in and tightened it down (but short of torque spec ) and it definitely still has some threads but it felt like it bottommed, with the head off.

Probably not going to work but my plan today is to see if I can find a helicoil kit to use for the one hole. (Frankly I’m concerned that maybe other Timesert will fail on the second 90degree)

I may be able to borrow a timesert kit from my local friendly Indy- more like rent- but he has no Serts. He’s a BMW specific shop that says he has done quite a few Timesert jobs and in his opinion the block is toast, that overheating has caused the aluminum to weaken.
Says I should replace the block- pretty far above my pay grade.

So, unless I can find a way to get the head on tight I’m looking at a new block, new engine or giving up on what was a bad idea to begin with.