I would use a new Autolite 26. You know that works.
AC-Delco spark plugs went out of business in 1962. GM buys the plugs that are labled AC from the cheapest vendor when they let contracts. Autolite, Champion (both owned by Ford) as well as NGK, Denso, or Bosch are what you will find inside an AC-Delco box today.
I just love reading about how a champion plug is trash compared to an AC plug, or an AC is much better than a NGK plug. A plug is a plug, despite what E3 says. They all work the same way; with the only difference being the heat range and the choice of metal used as the cathode in the plug (I prefer a platinum or iridium metal as they last a lot longer than copper, even though they cost more initially). All plugs made today are resistor plugs due to computerized ignitions that do not like static any more than your radio does.