Instructions for using a non-bundled web-server don't work

https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/nginx.md#using-a-non-bundled-web-server

I have installed GitLab (CE 7.10.0 using the Ominbus installation method) to a Ubuntu 14.04.2 server with a LAMP stack. The server in question also has Tomcat installed which is listening to port 8080.

GitLab works fine if I change the Unicorn port from 8080 to 8081 and the Nginx port from 80 to 81, but I need GitLab to be accessible via port 80. I have followed the instructions for using a non-bundled web-server to no avail. Though those instructions do not indicate that any Apache virtual host configuration is necessary I have tried several different proxy and virtual host configurations with no luck.

Any help with this configuration would be most appreciated.