If it is an extranet:
A) You need to set up a public IP for the server. You can do that in your firewall (it will do the NAT translation of the public IP to the internal network IP of the server)
B) In your firewall, you need to open port 8000 for that public IP.
C) On the client side: you need either to set up that IP:port in the desktop shortcut or menu, or add that entry to the hosts file.
D) I do not think you need to touch the app server at all
For an intranet:
You can use a VPN software or appliance to do the client IP NAT – this way you do not need to change the IP in your shortcut or hosts file. Plus, access is more secure.