58 impala convertible

I have recently picked up a 58 impala convertible, this car ha 2 quarter panel vents per side instead of one like I have seen on most others, is the second vent something someone has added?, or is it original on certain trim levels?,
Any info would be appreciated
Al

 

Can you post a pic?

All convertibles were Impalas, and all Impalas had the same trim.

 

You're talking about a GM Dealer accessory called Exhaust Ports.
Post pics of the car, are you selling it?