My theory as to why some folks installed them (three taillights per side) goes back to the full-size Chevys of 1958-(not 59)-60-61-62-63-64-65-66-67-68-69-70 and 71.
You'll remember that the lower models got two taillights per side, while the Impala got three. They were usually round.........sometimes rectangular.....sometimes odd shaped. But it was two or three depending on the model.
1960 Impala
1960 Biscayne
1968 Impala
1968 Biscayne
So, my theory is that some guys didn't want a "Biscayne" or "Bel-air" Corvette. They wanted an "Impala".
Me? I always preferred those sleeper Biscaynes anyway, so I left mine alone.
What's your theory?
You'll remember that the lower models got two taillights per side, while the Impala got three. They were usually round.........sometimes rectangular.....sometimes odd shaped. But it was two or three depending on the model.

1960 Impala

1960 Biscayne

1968 Impala

1968 Biscayne
So, my theory is that some guys didn't want a "Biscayne" or "Bel-air" Corvette. They wanted an "Impala".
Me? I always preferred those sleeper Biscaynes anyway, so I left mine alone.

What's your theory?