A link to my LinkedIn post to a blog with the how to is https://www.linkedin.com/pulse/blog-mash-up-virtualbox-port-forwards-windows-7-oracle-scott-nelson.
In short, go to advanced networking and add the port to the Virtualbox instance settings then go to the Firewall control in Oracle Linux System Administration menu and add it there, too.
One of those things that took hours to figure out and moments to explain.