Then you can’t use discourse-setup or you can run it with --skip-connection-test, but you’re on your own to make it work. You also need to comment out the ssl and https templates.
That won’t work.
You should first install it on a machine that doesn’t have anything else using ports 80 and 443 to see how it works. If you’re not going to do that then you need to understand how it works before you do anything.