I've had one side or the other off several times and 7 of the inserts look pretty good. One is a bit distorted but still doesn't leak - so maybe next time, or the time after or .... eventually

Torque?? Headers??? Tighten the bolts till they squeak then another half turn

I have the Split Bolt fasteners - those that cause the threaded end to expand when you snug down the insert. I have forgotten the torque figure off hand, but it is less then a solid ARP header bolt. They were the smallest diameter bolts (12 point) I could find that would work with the Sanderson Headers for the GT40P heads