If he doesn’t have enough money to be insurance, he doesn’t have enough money to pay for emergency health care and therefore represents an unnecessary burden to Thailand… and your friend should probably stay home.
The requirement for a OA visa criminal background check is about as vague as the check for elephantiasis. Go to your state LEO or county sheriff, not the FBI.
And yes, 40 year old criminal records can often be expunged. State laws are changing every year.