I just tried in the same VM, updating server.xml to listen on port 80 and updating /etc/default/tomcat6 to have AUTHBIND=yes tomcat6 then started on port 80 without any issue.
I just tried in the same VM, updating server.xml to listen on port 80 and updating /etc/default/ tomcat6 to have AUTHBIND=yes
tomcat6 then started on port 80 without any issue.