[Steeveedee]

The "2" could mean second shift. Casting iron is an around the clock job, because you can't just shut the furnace off Friday and walk away, to return on Monday. A lot of times, the casting will show a clock hour hand to indicate the time of some operation. If you haven't started your truck since replacing the heads, it is possible that the other head has that hole drilled and tapped for the AC bracket bolt, and you can switch the heads. Not sure about an engine of this vintage, but in later years, heads seem to be made to be interchangeable, with holes drilled and tapped everywhere. Given that GM tracked the cost to .1¢ for parts (when you buy millions of screws, for example, it makes sense), my guess here may be wrong.