Interesting, I didn't know the 1980 square light was just an option, thank you.
It was part of RPO V22 Deluxe Grille. Just like single or stacked head lamps in '81-'87('88), or single or side by side head lamps in "89-'91. It was also available '73-'79, but there were no head lamp differences.
It was included with the top trim level, or optional on any lower trim level. So all 1980 Silverados had square head lamps, and lower trim levels could have either,
Martin


