Just to update others to where I got with this:
27910 UDP to 27910 to the local IP of the machine, so the forwarding is correct. Previously, pball was blocked in windows firewall. The private ones are now allowed (both TCP and UDP) and it shows in serverlist.php (public ones are still blocked, same as my own setup). It however does not show in server browser, and cannot connect via the IP/port given on serverlist.php.