Sara,
On some Argosies there there are or were two antenna's on the roof. There was a TV antenna on all of them and some had CB antennas as well.
This side view of my Argosy shows the original TV antenna right in front of the air conditioner. I've since replaced that TV antenna for a more modern digital unit.
In this picture you can see the CB antenna is mounted to the front center marker light pod. I've only seen the CB antennas mounted like this on Argosies. I've not seen any Classics with CB antennas mounted on the light pod.
Here's a couple of pictures of the later Argosies with CB antennas mounted on the front center marker light pods.
As far as a replacement antenna
this one this one would probably work.
Brad