Not sure where you get those numbers from, but I'd say they're optimistic. Never seen any 'aux' tanks for a 320, but not sure it would help anyway due weight issues.
Couple of facts:
77t MTOW
18.7t (max fuel)
58.3t left over....
45t operating empty weight.
13.3t left over for whatever you want to fill it with.....
No idea what TT standard pax weight is but 82 seems to be the going rate with 14 kg bag per pax.
Me thinks around 139 seats on a 180 seat aircraft. 77% capacity
Fuel. 18.7 max
-1.3 fixed
-1.0 variable
16.4 left.
Burn 2.4t per/hour(absolute BEST case) = 6.8hrs range in nil wind
A bit 'toit' with any holding in Bali or wx north of AS!
So on paper it's doable, but not really set up for this run in seat numbers or fuel capacity.
Not sure the sharklets do 4/5th's of F$&k all for any fuel savings, but they do look keeeewl.