sure looks like a heli-coil to me.
i have only installed thousands upon thousands in my working life, and i agree, a time-sert or keen-sert would have been the better repair.
Yes, that is a heli-coil, my shop at that time (they were in business since the father opened right after returning from WW2 - yup, that long, and only closed recently - 2 maybe 3 years ago) was very comfortable doing this, in fact they had asked me if I had a specific preference as to how to fix this, and given that my intended build was a street motor with up to 400hp (power goals at that time), they said this would work!
The non heli-coil mains also showed some cap walk, but to an amateur eye like mine I honestly couldn't tell if what was there was a BIG deal, or just a 'normal thing' you might see in these kind of factory builds.
