Hello trumpetradio,
You can make Centova Cast listen on port 80, that is not an issue, however you cannot have two programs use the same port on the same IP address. This is a fundamental limitation of the Internet protocol's (IP) transport layer.
In other words, you would need two separate public IP addresses, one for Apache and one of Centova Cast's web service.
Once you have a free public IP address for Centova Cast alone, then you can simply add the following line to "/usr/local/centovacast/etc/cc-panel.conf"
listen 80
Then restart Centova Cast (/usr/local/centovacast/centovacast restart).
Regards.