Looks like it's a mixed bag on the earlier cars. None of mine were 1/2 bolts.
The /6 cars I had were tow package cars. Maybe someone with a 67-69 parts book can look in section 17, 17-17-4 IIRC to see if there is more than one spring bolt number bolt for those years. I know the 70-72 cars have one bolt number.
