Well to answer my own Q'
It worked , portforwarding 8443 to 443 , and use the WAN ip address as the NAT ip address.
As i accessed the "site" via https://x.x.x.x:8443 , i got hit by a: HTTP_REFERER Error (and a RED Screen , leaving me "dead there") , after authenticating on the login page.
Luckily i could still access the GUI via L2L VPN , but you might want think about that issue, to not be locked out.
I had to add x.x.x.x to System -> Advanced -> Admin access -> Alternate Hostnames
As i did not want to disable : Browser HTTP_REFERER enforcement
/Bingo