External access to Yun - request not recognised as HTML
It works!

The changes to the uhttpd must have done the trick to listen for http traffic on a given IP/port (other than 0.0.0.0:80).

Instead of supplying a port number for the server in the code, I would surmise that the change to the config takes care of it so this, so the port number in code is no longer needed:

YunServer server(XXXXX);

should be changed back to 

YunServer server;